Cellular graphene films

ABSTRACT

The present disclosure provides supercapacitors that may avoid the shortcomings of current energy storage technology. Provided herein are electrochemical systems, comprising three dimensional porous reduced graphene oxide film electrodes. Prototype supercapacitors disclosed herein may exhibit improved performance compared to commercial supercapacitors. Additionally, the present disclosure provides a simple, yet versatile technique for the fabrication of supercapacitors through the direct preparation of three dimensional porous reduced graphene oxide films by filtration and freeze casting.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/382,871, filed Dec. 19, 2016, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/271,115, filed Dec. 22, 2015,and claims the benefit of U.S. Provisional Patent Application Ser. No.62/428,608, filed Dec. 1, 2016, the disclosures of which are herebyincorporated herein by reference in their entireties.

BACKGROUND

As a result of the rapidly growing energy needs of modern life, thedevelopment of high performance energy storage devices has gainedsignificant attention. Supercapacitors are promising energy storagedevices with properties intermediate between those of batteries andtraditional capacitors, but they are being improved more rapidly thaneither. Over the past couple of decades, supercapacitors have become keycomponents of everyday products by replacing batteries and capacitors inan increasing number of applications. Their high power density andexcellent low temperature performance have made them the technology ofchoice for back-up power, cold starting, flash cameras, regenerativebraking and hybrid electric vehicles. The future growth of thistechnology depends on further improvements in energy density, powerdensity, calendar and cycle life and production cost.

SUMMARY

The instant inventors have recognized and provided a solution to theneed for higher performance energy storage devices. Provided herein aregraphene materials, compositions of matter, fabrication processes anddevices with improved performance.

The applications described herein provide for improvements in the areasof flexible electronics such as solar cell arrays, flexible displays andwearable electronics, as well as an increase in energy storage systemswith high power densities. Many conventional supercapacitors exhibit lowenergy densities, and rigid form factors which break or degrade byrepeated bending. While normal electronic devices have seen very rapidprogress following Moore's law, energy storage devices have advancedonly slightly because of the lack of new materials with high chargestorage capacity.

The present disclosure provides supercapacitors that may avoidshortcomings of current energy storage technology. Provided herein arematerials and fabrication processes of such supercapacitors. In someembodiments, an electrochemical system comprising a first electrode, asecond electrode, wherein at least one of the first electrode and thesecond electrode comprises a three dimensional porous reduced grapheneoxide film. In some embodiments, the electrochemical system furthercomprises an electrolyte disposed between the first electrode and thesecond electrode. In some embodiments, the electrolyte is an aqueouselectrolyte. In some embodiments, the electrochemical system furthercomprises a separator disposed between the first electrode and thesecond electrode. In some embodiments, the electrochemical systemfurther comprises a current collector.

In some embodiments, the present disclosure provides three dimensionalporous reduced graphene oxide films that may avoid the shortcomings ofcurrent supercapacitor technology. Prototype supercapacitors disclosedherein may exhibit improved performance compared to commercialsupercapacitors. In some embodiments, the supercapacitor devicesdescribed herein exhibit power densities in excess of twice the powerdensity of commercial supercapacitors. In certain embodiments, thesupercapacitor devices described herein not only exhibit power densitiesin excess of twice the power density of commercial supercapacitors, butalso may also be charged and discharged in excess of 50% less time.

In some embodiments, the present disclosure provides a simple, yetversatile technique for the fabrication of supercapacitors. In someembodiments, the present disclosure provides a method of fabrication ofa supercapacitor electrode. In some embodiments, the fabrication methodof such a supercapacitor electrode is based on method for the directpreparation of reduced graphene oxide. In some embodiments, thefabrication method of such a supercapacitor electrode is based on methodfor the filtration of reduced graphene oxide. In some embodiments, thefabrication method of such a supercapacitor electrode is based on methodfor freeze casting reduced graphene oxide. In some embodiments, thefabrication method produces an electrode comprising three dimensionalporous reduced graphene oxide films.

One aspect provided herein is an electrode comprising a reduced grapheneoxide film wherein the graphene oxide film has a thickness of about 1 μmto about 4 μm. In some embodiments, the graphene oxide film has a doublelayer capacitance of at least about 10 μF/cm². In some embodiments, thegraphene oxide film has a double layer capacitance of at most about 35μF/cm². In some embodiments, the graphene oxide film has a double layercapacitance of about 10 μF/cm² to about 35 μF/cm². In some embodiments,the graphene oxide film has a double layer capacitance of about 10mF/cm² to about 15 mF/cm², about 10 mF/cm² to about 20 mF/cm², about 10mF/cm² to about 25 mF/cm², about 10 mF/cm² to about 30 mF/cm², about 10mF/cm² to about 35 mF/cm², about 15 mF/cm² to about 20 mF/cm², about 15mF/cm² to about 25 mF/cm², about 15 mF/cm² to about 30 mF/cm², about 15mF/cm² to about 35 mF/cm², about 20 mF/cm² to about 25 mF/cm², about 20mF/cm² to about 30 mF/cm², about 20 mF/cm² to about 35 mF/cm², about 25mF/cm² to about 30 mF/cm², about 25 mF/cm² to about 35 mF/cm² or about30 mF/cm² to about 35 mF/cm².

In some embodiments the graphene oxide film has a characteristic timeconstant of at least about 45 seconds. In some embodiments, the grapheneoxide film has a characteristic time constant of at most about 150seconds. In some embodiments, the graphene oxide film has acharacteristic time constant of about 45 to about 150. In someembodiments the graphene oxide film has a characteristic time constantof about 45 seconds to about 50 seconds, about 45 seconds to about 60seconds, about 45 seconds to about 70 seconds, about 45 seconds to about80 seconds, about 45 seconds to about 90 seconds, about 45 seconds toabout 100 seconds, about 45 seconds to about 120 seconds, about 45seconds to about 130 seconds, about 45 seconds to about 140 seconds,about 45 seconds to about 150 seconds, about 50 seconds to about 60seconds, about 50 seconds to about 70 seconds, about 50 seconds to about80 seconds, about 50 seconds to about 90 seconds, about 50 seconds toabout 100 seconds, about 50 seconds to about 120 seconds, about 50seconds to about 130 seconds, about 50 seconds to about 140 seconds,about 50 seconds to about 150 seconds, about 60 seconds to about 70seconds, about 60 seconds to about 80 seconds, about 60 seconds to about90 seconds, about 60 seconds to about 100 seconds, about 60 seconds toabout 120 seconds, about 60 seconds to about 130 seconds, about 60seconds to about 140 seconds, about 60 seconds to about 150 seconds,about 70 seconds to about 80 seconds, about 70 seconds to about 90seconds, about 70 seconds to about 100 seconds, about 70 seconds toabout 120 seconds, about 70 seconds to about 130 seconds, about 70seconds to about 140 seconds, about 70 seconds to about 150 seconds,about 80 seconds to about 90 seconds, about 80 seconds to about 100seconds, about 80 seconds to about 120 seconds, about 80 seconds toabout 130 seconds, about 80 seconds to about 140 seconds, about 80seconds to about 150 seconds, about 90 seconds to about 100 seconds,about 90 seconds to about 120 seconds, about 90 seconds to about 130seconds, about 90 seconds to about 140 seconds, about 90 seconds toabout 150 seconds, about 100 seconds to about 120 seconds, about 100seconds to about 130 seconds, about 100 seconds to about 140 seconds,about 100 seconds to about 150 seconds, about 120 seconds to about 130seconds, about 120 seconds to about 140 seconds, about 120 seconds toabout 150 seconds, about 130 seconds to about 140 seconds, about 130seconds to about 150 seconds or about 140 seconds to about 150 seconds.

In some embodiments the graphene oxide film has a sheet resistance of atleast about 0.125Ω. In some embodiments, the graphene oxide film has asheet resistance of at most about 0.5Ω. In some embodiments, thegraphene oxide film has a sheet resistance of about 0.125Ω to about0.5Ω. In some embodiments the graphene oxide film has a sheet resistanceof about 0.125Ω to about 0.1875Ω, about 0.125Ω to about 0.25Ω, about0.125Ω to about 0.3125Ω, about 0.125Ω to about 0.375Ω, about 0.125Ω toabout 0.4375Ω, about 0.125Ω to about 0.5Ω, about 0.1875Ω to about 0.25Ω,about 0.1875Ω to about 0.3125Ω, about 0.1875Ω to about 0.375Ω, about0.1875Ω to about 0.4375Ω, about 0.1875Ω to about 0.5Ω, about 0.25Ω toabout 0.3125Ω, about 0.25Ω to about 0.375Ω, about 0.25Ω to about0.4375Ω, about 0.25Ω to about 0.5Ω, about 0.3125Ω to about 0.375Ω, about0.3125Ω to about 0.4375Ω, about 0.3125Ω to about 0.5Ω, about 0.375Ω toabout 0.4375Ω, about 0.375Ω to about 0.5Ω or about 0.4375Ω to about0.5Ω.

In some embodiments the graphene oxide film has a charge transportresistance of at least about 0.5Ω. In some embodiments, the grapheneoxide film has a charge transport resistance of at most about 2Ω. Insome embodiments, the graphene oxide film has a charge transportresistance of about 0.5Ω to about 2Ω. In some embodiments the grapheneoxide film has a charge transport resistance of about 0.5Ω to about0.6Ω, about 0.5Ω to about 0.7Ω, about 0.5Ω to about 0.8Ω, about 0.5Ω toabout 0.9Ω, about 0.5Ω to about 1Ω, about 0.5Ω to about 1.25Ω, about0.5Ω to about 1.5Ω, about 0.5Ω to about 1.75Ω, about 0.5Ω to about 2Ω,about 0.6Ω to about 0.7Ω, about 0.6Ω to about 0.8Ω, about 0.6Ω to about0.9Ω, about 0.6Ω to about 1Ω, about 0.6Ω to about 1.25Ω, about 0.6Ω toabout 1.5Ω, about 0.6Ω to about 1.75Ω, about 0.6Ω to about 2Ω, about0.7Ω to about 0.8Ω, about 0.7Ω to about 0.9Ω, about 0.7Ω to about 1Ω,about 0.7Ω to about 1.25Ω, about 0.7Ω to about 1.5Ω, about 0.7Ω to about1.75Ω, about 0.7Ω to about 2Ω, about 0.8Ω to about 0.9Ω, about 0.8Ω toabout 1Ω, about 0.8Ω to about 1.25Ω, about 0.8Ω to about 1.5Ω, about0.8Ω to about 1.75Ω, about 0.8Ω to about 2Ω, about 0.9Ω to about 1Ω,about 0.9Ω to about 1.25Ω, about 0.9Ω to about 1.5Ω, about 0.9Ω to about1.75Ω, about 0.9Ω to about 2Ω, about 1Ω to about 1.25Ω, about 1Ω toabout 1.5Ω, about 1Ω to about 1.75Ω, about 1Ω to about 2Ω, about 1.25Ωto about 1.5Ω, about 1.25Ω to about 1.75Ω, about 1.25Ω to about 2Ω,about 1.5Ω to about 1.75Ω, about 1.5Ω to about 2Ω or about 1.75Ω toabout 2Ω.

In some embodiments the graphene oxide film has a charge transportresistance of at least about 10 kΩ. In some embodiments, the grapheneoxide film has a charge transport resistance of at most about 45 kΩ. Insome embodiments, the graphene oxide film has a charge transportresistance of about 10 kΩ to about 45 kΩ. In some embodiments thegraphene oxide film has a charge transport resistance of about 10 kΩ toabout 15 kΩ about 10 kΩ to about 20 kΩ about 10 kΩ to about 25 kΩ, about10 kΩ to about 30 kΩ, about 10 kΩ to about 35 kΩ, about 10 kΩ to about40 kΩ about 10 kΩ to about 45 kΩ, about 15 kΩ to about 20 kΩ about 15 kΩto about 25 kΩ about 15 kΩ to about 30 kΩ about 15 kΩ to about 35 kΩabout 15 kΩ to about 40 kΩ, about 15 kΩ to about 45 kΩ about 20 kΩ toabout 25 kΩ about 20 kΩ to about 30 kΩ about 20 kΩ to about 35 kΩ about20 kΩ to about 40 kΩ about 20 kΩ to about 45 kΩ about 25 kΩ to about 30kΩ about 25 kΩ to about 35 la about 25 kΩ to about 40 kΩ about 25 kΩ toabout 45 kΩ, about 30 kΩ to about 35 kΩ about 30 kΩ to about 40 kΩ about30 kΩ to about 45 kΩ about 35 kΩ to about 40 kΩ about 35 kΩ to about 45kΩ or about 40 kΩ to about 45 kΩ.

In some embodiments the graphene oxide film has a charge transportresistance of at least about 35. In some embodiments, the graphene oxidefilm has a charge transport resistance of at most about 120. In someembodiments, the graphene oxide film has a charge transport resistanceof about 35 to about 120. In some embodiments the graphene oxide filmhas a charge transport resistance of about 35 S^(−n) to about 45 S^(−n),about 35 S^(−n) to about 55 S^(−n), about 35 S^(−n) to about 65 S^(−n),about 35 S^(−n) to about 75 S^(−n), about 35 S^(−n) to about 85 S^(−n),about 35 S^(−n) to about 95 S^(−n), about 35 S^(−n) to about 100 S^(−n),about 35 S^(−n) to about 110 S^(−n), about 35 S^(−n) to about 120S^(−n), about 45 S^(−n) to about 55 S^(−n), about 45 S^(−n) to about 65S^(−n), about 45 S^(−n) to about 75 S^(−n), about 45 S^(−n) to about 85S^(−n), about 45 S^(−n) to about 95 S^(−n), about 45 S^(−n) to about 100S^(−n), about 45 S^(−n) to about 110 S^(−n), about 45 S^(−n) to about120 S^(−n), about 55 S^(−n) to about 65 S^(−n), about 55 S^(−n) to about75 S^(−n), about 55 S^(−n) to about 85 S^(−n), about 55 S^(−n) to about95 S^(n), about 55 S^(−n) to about 100 S^(−n), about 55 S^(−n) to about110 S^(−n), about 55 S^(−n) to about 120 S^(−n), about 65 S^(−n) toabout 75 S^(−n), about 65 S^(−n) to about 85 S^(−n), about 65 S^(−n) toabout 95 S^(−n), about 65 S^(−n) to about 100 S^(−n), about 65 S^(−n) toabout 110 S^(−n), about 65 S^(−n) to about 120 S^(−n), about 75 S^(−n)to about 85 S^(−n), about 75 S^(−n) to about 95 S^(−n), about 75 S^(−n)to about 100 S^(−n), about 75 S^(−n) to about 110 S^(−n), about 75S^(−n) to about 120 S^(−n), about 85 S^(−n) to about 95 S^(−n), about 85S^(−n) to about 100 S^(−n), about 85 S^(−n) to about 110 S^(−n), about85 S^(−n) to about 120 S^(−n), about 95 S^(−n) to about 100 S^(−n),about 95 S^(−n) to about 110 S^(−n), about 95 S^(−n) to about 120S^(−n), about 100 S^(−n) to about 110 S^(−n), about 100 S^(−n) to about120 S^(−n) or about 110 S^(−n) to about 120 S^(−n).

In some embodiments the graphene oxide film has a constant phase elementexponent of at least about 0.1. In some embodiments, the graphene oxidefilm has a constant phase element exponent of at most about 0.6. In someembodiments, the graphene oxide film has a constant phase elementexponent of about 0.1 to about 0.6. In some embodiments the grapheneoxide film has a constant phase element exponent of about 0.1 to about0.2, about 0.1 to about 0.3, about 0.1 to about 0.4, about 0.1 to about0.5, about 0.1 to about 0.6, about 0.2 to about 0.3, about 0.2 to about0.4, about 0.2 to about 0.5, about 0.2 to about 0.6, about 0.3 to about0.4, about 0.3 to about 0.5, about 0.3 to about 0.6, about 0.4 to about0.5, about 0.4 to about 0.6 or about 0.5 to about 0.6.

In some embodiments the graphene oxide film has a feedback capacitanceof at least about 50 F/g. In some embodiments, the graphene oxide filmhas a feedback capacitance of at most about 200 F/g. In someembodiments, the graphene oxide film has a feedback capacitance of isabout 50 F/g to about 200 F/g. In some embodiments the graphene oxidefilm has a feedback capacitance of is about 50 F/g to about 60 F/g,about 50 F/g to about 70 F/g, about 50 F/g to about 80 F/g, about 50 F/gto about 90 F/g, about 50 F/g to about 100 F/g, about 50 F/g to about120 F/g, about 50 F/g to about 140 F/g, about 50 F/g to about 160 F/g,about 50 F/g to about 180 F/g, about 50 F/g to about 200 F/g, about 60F/g to about 70 F/g, about 60 F/g to about 80 F/g, about 60 F/g to about90 F/g, about 60 F/g to about 100 F/g, about 60 F/g to about 120 F/g,about 60 F/g to about 140 F/g, about 60 F/g to about 160 F/g, about 60F/g to about 180 F/g, about 60 F/g to about 200 F/g, about 70 F/g toabout 80 F/g, about 70 F/g to about 90 F/g, about 70 F/g to about 100F/g, about 70 F/g to about 120 F/g, about 70 F/g to about 140 F/g, about70 F/g to about 160 F/g, about 70 F/g to about 180 F/g, about 70 F/g toabout 200 F/g, about 80 F/g to about 90 F/g, about 80 F/g to about 100F/g, about 80 F/g to about 120 F/g, about 80 F/g to about 140 F/g, about80 F/g to about 160 F/g, about 80 F/g to about 180 F/g, about 80 F/g toabout 200 F/g, about 90 F/g to about 100 F/g, about 90 F/g to about 120F/g, about 90 F/g to about 140 F/g, about 90 F/g to about 160 F/g, about90 F/g to about 180 F/g, about 90 F/g to about 200 F/g, about 100 F/g toabout 120 F/g, about 100 F/g to about 140 F/g, about 100 F/g to about160 F/g, about 100 F/g to about 180 F/g, about 100 F/g to about 200 F/g,about 120 F/g to about 140 F/g, about 120 F/g to about 160 F/g, about120 F/g to about 180 F/g, about 120 F/g to about 200 F/g, about 140 F/gto about 160 F/g, about 140 F/g to about 180 F/g, about 140 F/g to about200 F/g, about 160 F/g to about 180 F/g, about 160 F/g to about 200 F/gor about 180 F/g to about 200 F/g.

In some embodiments the graphene oxide film has a conductivity of atleast about 5 S/m. In some embodiments, the graphene oxide film has aconductivity of at most about 20 S/m. In some embodiments, the grapheneoxide film has a conductivity of about 5 S/m to about 20 S/m. In someembodiments the graphene oxide film has a conductivity of about 5 S/m toabout 6 S/m, about 5 S/m to about 7 S/m, about 5 S/m to about 8 S/m,about 5 S/m to about 9 S/m, about 5 S/m to about 10 S/m, about 5 S/m toabout 12 S/m, about 5 S/m to about 14 S/m, about 5 S/m to about 16 S/m,about 5 S/m to about 18 S/m, about 5 S/m to about 20 S/m, about 6 S/m toabout 7 S/m, about 6 S/m to about 8 S/m, about 6 S/m to about 9 S/m,about 6 S/m to about 10 S/m, about 6 S/m to about 12 S/m, about 6 S/m toabout 14 S/m, about 6 S/m to about 16 S/m, about 6 S/m to about 18 S/m,about 6 S/m to about 20 S/m, about 7 S/m to about 8 S/m, about 7 S/m toabout 9 S/m, about 7 S/m to about 10 S/m, about 7 S/m to about 12 S/m,about 7 S/m to about 14 S/m, about 7 S/m to about 16 S/m, about 7 S/m toabout 18 S/m, about 7 S/m to about 20 S/m, about 8 S/m to about 9 S/m,about 8 S/m to about 10 S/m, about 8 S/m to about 12 S/m, about 8 S/m toabout 14 S/m, about 8 S/m to about 16 S/m, about 8 S/m to about 18 S/m,about 8 S/m to about 20 S/m, about 9 S/m to about 10 S/m, about 9 S/m toabout 12 S/m, about 9 S/m to about 14 S/m, about 9 S/m to about 16 S/m,about 9 S/m to about 18 S/m, about 9 S/m to about 20 S/m, about 10 S/mto about 12 S/m, about 10 S/m to about 14 S/m, about 10 S/m to about 16S/m, about 10 S/m to about 18 S/m, about 10 S/m to about 20 S/m, about12 S/m to about 14 S/m, about 12 S/m to about 16 S/m, about 12 S/m toabout 18 S/m, about 12 S/m to about 20 S/m, about 14 S/m to about 16S/m, about 14 S/m to about 18 S/m, about 14 S/m to about 20 S/m, about16 S/m to about 18 S/m, about 16 S/m to about 20 S/m or about 18 S/m toabout 20 S/m.

In some embodiments the graphene oxide film has an areal mass loading ofat least about 0.1 mg/cm². In some embodiments, the graphene oxide filmhas an areal mass loading of at most about 0.5 mg/cm². In someembodiments, the graphene oxide film has an areal mass loading of about0.1 mg/cm² to about 0.5 mg/cm². In some embodiments the graphene oxidefilm has an areal mass loading of about 0.1 mg/cm² to about 0.2 mg/cm²,about 0.1 mg/cm² to about 0.3 mg/cm², about 0.1 mg/cm² to about 0.4mg/cm², about 0.1 mg/cm² to about 0.5 mg/cm², about 0.2 mg/cm² to about0.3 mg/cm², about 0.2 mg/cm² to about 0.4 mg/cm², about 0.2 mg/cm² toabout 0.5 mg/cm², about 0.3 mg/cm² to about 0.4 mg/cm², about 0.3 mg/cm²to about 0.5 mg/cm² or about 0.4 mg/cm² to about 0.5 mg/cm².

In some embodiments the graphene oxide film has an active density of atleast about 0.5 mg/cm³. In some embodiments, the graphene oxide film hasan active density of at most about 2 mg/cm³. In some embodiments, thegraphene oxide film has an active density of about 0.5 mg/cm³ to about 2mg/cm³. In some embodiments the graphene oxide film has an activedensity of about 0.5 mg/cm³ to about 0.75 mg/cm³, about 0.5 mg/cm³ toabout 1 mg/cm³, about 0.5 mg/cm³ to about 1.25 mg/cm³, about 0.5 mg/cm³to about 1.5 mg/cm³, about 0.5 mg/cm³ to about 1.75 mg/cm³, about 0.5mg/cm³ to about 2 mg/cm³, about 0.75 mg/cm³ to about 1 mg/cm³, about0.75 mg/cm³ to about 1.25 mg/cm³, about 0.75 mg/cm³ to about 1.5 mg/cm³,about 0.75 mg/cm³ to about 1.75 mg/cm³, about 0.75 mg/cm³ to about 2mg/cm³, about 1 mg/cm³ to about 1.25 mg/cm³, about 1 mg/cm³ to about 1.5mg/cm³, about 1 mg/cm³ to about 1.75 mg/cm³, about 1 mg/cm³ to about 2mg/cm³, about 1.25 mg/cm³ to about 1.5 mg/cm³, about 1.25 mg/cm³ toabout 1.75 mg/cm³, about 1.25 mg/cm³ to about 2 mg/cm³, about 1.5 mg/cm³to about 1.75 mg/cm³, about 1.5 mg/cm³ to about 2 mg/cm³ or about 1.75mg/cm³ to about 2 mg/cm³.

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at least about 90F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at most about 360F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of about 90 F/g toabout 360 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 1 A/g, of about90 F/g to about 120 F/g, about 90 F/g to about 150 F/g, about 90 F/g toabout 180 F/g, about 90 F/g to about 210 F/g, about 90 F/g to about 240F/g, about 90 F/g to about 270 F/g, about 90 F/g to about 300 F/g, about90 F/g to about 360 F/g, about 120 F/g to about 150 F/g, about 120 F/gto about 180 F/g, about 120 F/g to about 210 F/g, about 120 F/g to about240 F/g, about 120 F/g to about 270 F/g, about 120 F/g to about 300 F/g,about 120 F/g to about 360 F/g, about 150 F/g to about 180 F/g, about150 F/g to about 210 F/g, about 150 F/g to about 240 F/g, about 150 F/gto about 270 F/g, about 150 F/g to about 300 F/g, about 150 F/g to about360 F/g, about 180 F/g to about 210 F/g, about 180 F/g to about 240 F/g,about 180 F/g to about 270 F/g, about 180 F/g to about 300 F/g, about180 F/g to about 360 F/g, about 210 F/g to about 240 F/g, about 210 F/gto about 270 F/g, about 210 F/g to about 300 F/g, about 210 F/g to about360 F/g, about 240 F/g to about 270 F/g, about 240 F/g to about 300 F/g,about 240 F/g to about 360 F/g, about 270 F/g to about 300 F/g, about270 F/g to about 360 F/g or about 300 F/g to about 360 F/g.

In some embodiments the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at least about 80F/g. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at most about 360F/g. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of about 80 F/g toabout 360 F/g. In some embodiments the graphene oxide film has avolumetric capacitance, in a current density of about 1 A/g, of about 80F/g to about 120 F/g, about 80 F/g to about 150 F/g, about 80 F/g toabout 180 F/g, about 80 F/g to about 210 F/g, about 80 F/g to about 240F/g, about 80 F/g to about 270 F/g, about 80 F/g to about 300 F/g, about80 F/g to about 360 F/g, about 120 F/g to about 150 F/g, about 120 F/gto about 180 F/g, about 120 F/g to about 210 F/g, about 120 F/g to about240 F/g, about 120 F/g to about 270 F/g, about 120 F/g to about 300 F/g,about 120 F/g to about 360 F/g, about 150 F/g to about 180 F/g, about150 F/g to about 210 F/g, about 150 F/g to about 240 F/g, about 150 F/gto about 270 F/g, about 150 F/g to about 300 F/g, about 150 F/g to about360 F/g, about 180 F/g to about 210 F/g, about 180 F/g to about 240 F/g,about 180 F/g to about 270 F/g, about 180 F/g to about 300 F/g, about180 F/g to about 360 F/g, about 210 F/g to about 240 F/g, about 210 F/gto about 270 F/g, about 210 F/g to about 300 F/g, about 210 F/g to about360 F/g, about 240 F/g to about 270 F/g, about 240 F/g to about 300 F/g,about 240 F/g to about 360 F/g, about 270 F/g to about 300 F/g, about270 F/g to about 360 F/g, or about 300 F/g to about 360 F/g.

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of at least about 25F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of at most about 100F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of about 25 F/g toabout 100 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 500 A/g, of about25 F/g to about 30 F/g, about 25 F/g to about 40 F/g, about 25 F/g toabout 50 F/g, about 25 F/g to about 60 F/g, about 25 F/g to about 70F/g, about 25 F/g to about 80 F/g, about 25 F/g to about 90 F/g, about25 F/g to about 100 F/g, about 30 F/g to about 40 F/g, about 30 F/g toabout 50 F/g, about 30 F/g to about 60 F/g, about 30 F/g to about 70F/g, about 30 F/g to about 80 F/g, about 30 F/g to about 90 F/g, about30 F/g to about 100 F/g, about 40 F/g to about 50 F/g, about 40 F/g toabout 60 F/g, about 40 F/g to about 70 F/g, about 40 F/g to about 80F/g, about 40 F/g to about 90 F/g, about 40 F/g to about 100 F/g, about50 F/g to about 60 F/g, about 50 F/g to about 70 F/g, about 50 F/g toabout 80 F/g, about 50 F/g to about 90 F/g, about 50 F/g to about 100F/g, about 60 F/g to about 70 F/g, about 60 F/g to about 80 F/g, about60 F/g to about 90 F/g, about 60 F/g to about 100 F/g, about 70 F/g toabout 80 F/g, about 70 F/g to about 90 F/g, about 70 F/g to about 100F/g, about 80 F/g to about 90 F/g, about 80 F/g to about 100 F/g orabout 90 F/g to about 100 F/g.

In some embodiments the graphene oxide film has a capacitive retention,after about 1000 cycles of charging, of at least about 40%. In someembodiments, the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of at most about 98%. In someembodiments, the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of about 40% to about 98%. In someembodiments the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of about 40% to about 50%, about 40% toabout 60%, about 40% to about 70%, about 40% to about 80%, about 40% toabout 90%, about 40% to about 98%, about 50% to about 60%, about 50% toabout 70%, about 50% to about 80%, about 50% to about 90%, about 50% toabout 98%, about 60% to about 70%, about 60% to about 80%, about 60% toabout 90%, about 60% to about 98%, about 70% to about 80%, about 70% toabout 90%, about 70% to about 98%, about 80% to about 90%, about 80% toabout 98% or about 90% to about 98%.

In some embodiments the graphene oxide film has a gravimetric energydensity of at least about 3 Wh/kg. In some embodiments, the grapheneoxide film has a gravimetric energy density of at most about 12 Wh/kg.In some embodiments, the graphene oxide film has a gravimetric energydensity of about 3 Wh/kg to about 12 Wh/kg. In some embodiments thegraphene oxide film has a gravimetric energy density of about 3 Wh/kg toabout 4 Wh/kg, about 3 Wh/kg to about 5 Wh/kg, about 3 Wh/kg to about 6Wh/kg, about 3 Wh/kg to about 7 Wh/kg, about 3 Wh/kg to about 8 Wh/kg,about 3 Wh/kg to about 9 Wh/kg, about 3 Wh/kg to about 10 Wh/kg, about 3Wh/kg to about 11 Wh/kg, about 3 Wh/kg to about 12 Wh/kg, about 4 Wh/kgto about 5 Wh/kg, about 4 Wh/kg to about 6 Wh/kg, about 4 Wh/kg to about7 Wh/kg, about 4 Wh/kg to about 8 Wh/kg, about 4 Wh/kg to about 9 Wh/kg,about 4 Wh/kg to about 10 Wh/kg, about 4 Wh/kg to about 11 Wh/kg, about4 Wh/kg to about 12 Wh/kg, about 5 Wh/kg to about 6 Wh/kg, about 5 Wh/kgto about 7 Wh/kg, about 5 Wh/kg to about 8 Wh/kg, about 5 Wh/kg to about9 Wh/kg, about 5 Wh/kg to about 10 Wh/kg, about 5 Wh/kg to about 11Wh/kg, about 5 Wh/kg to about 12 Wh/kg, about 6 Wh/kg to about 7 Wh/kg,about 6 Wh/kg to about 8 Wh/kg, about 6 Wh/kg to about 9 Wh/kg, about 6Wh/kg to about 10 Wh/kg, about 6 Wh/kg to about 11 Wh/kg, about 6 Wh/kgto about 12 Wh/kg, about 7 Wh/kg to about 8 Wh/kg, about 7 Wh/kg toabout 9 Wh/kg, about 7 Wh/kg to about 10 Wh/kg, about 7 Wh/kg to about11 Wh/kg, about 7 Wh/kg to about 12 Wh/kg, about 8 Wh/kg to about 9Wh/kg, about 8 Wh/kg to about 10 Wh/kg, about 8 Wh/kg to about 11 Wh/kg,about 8 Wh/kg to about 12 Wh/kg, about 9 Wh/kg to about 10 Wh/kg, about9 Wh/kg to about 11 Wh/kg, about 9 Wh/kg to about 12 Wh/kg, about 10Wh/kg to about 11 Wh/kg, about 10 Wh/kg to about 12 Wh/kg or about 11Wh/kg to about 12 Wh/kg.

In some embodiments the graphene oxide film has a volumetric energydensity of at least about 3 Wh/L. In some embodiments, the grapheneoxide film has a volumetric energy density of at most about 12 Wh/L. Insome embodiments, the graphene oxide film has a volumetric energydensity of about 3 Wh/L to about 12 Wh/L. In some embodiments thegraphene oxide film has a volumetric energy density of about 3 Wh/L toabout 4 Wh/L, about 3 Wh/L to about 5 Wh/L, about 3 Wh/L to about 6Wh/L, about 3 Wh/L to about 7 Wh/L, about 3 Wh/L to about 8 Wh/L, about3 Wh/L to about 9 Wh/L, about 3 Wh/L to about 10 Wh/L, about 3 Wh/L toabout 11 Wh/L, about 3 Wh/L to about 12 Wh/L, about 4 Wh/L to about 5Wh/L, about 4 Wh/L to about 6 Wh/L, about 4 Wh/L to about 7 Wh/L, about4 Wh/L to about 8 Wh/L, about 4 Wh/L to about 9 Wh/L, about 4 Wh/L toabout 10 Wh/L, about 4 Wh/L to about 11 Wh/L, about 4 Wh/L to about 12Wh/L, about 5 Wh/L to about 6 Wh/L, about 5 Wh/L to about 7 Wh/L, about5 Wh/L to about 8 Wh/L, about 5 Wh/L to about 9 Wh/L, about 5 Wh/L toabout 10 Wh/L, about 5 Wh/L to about 11 Wh/L, about 5 Wh/L to about 12Wh/L, about 6 Wh/L to about 7 Wh/L, about 6 Wh/L to about 8 Wh/L, about6 Wh/L to about 9 Wh/L, about 6 Wh/L to about 10 Wh/L, about 6 Wh/L toabout 11 Wh/L, about 6 Wh/L to about 12 Wh/L, about 7 Wh/L to about 8Wh/L, about 7 Wh/L to about 9 Wh/L, about 7 Wh/L to about 10 Wh/L, about7 Wh/L to about 11 Wh/L, about 7 Wh/L to about 12 Wh/L, about 8 Wh/L toabout 9 Wh/L, about 8 Wh/L to about 10 Wh/L, about 8 Wh/L to about 11Wh/L, about 8 Wh/L to about 12 Wh/L, about 9 Wh/L to about 10 Wh/L,about 9 Wh/L to about 11 Wh/L, about 9 Wh/L to about 12 Wh/L, about 10Wh/L to about 11 Wh/L, about 10 Wh/L to about 12 Wh/L or about 11 Wh/Lto about 12 Wh/L.

In some embodiments the graphene oxide film has a gravimetric powerdensity of at least about 35 kW/kg. In some embodiments, the grapheneoxide film has a gravimetric power density of at most about 140 kW/kg.In some embodiments, the graphene oxide film has a gravimetric powerdensity of about 35 kW/kg to about 140 kW/kg. In some embodiments thegraphene oxide film has a gravimetric power density of about 35 kW/kg toabout 55 kW/kg, about 35 kW/kg to about 75 kW/kg, about 35 kW/kg toabout 95 kW/kg, about 35 kW/kg to about 110 kW/kg, about 35 kW/kg toabout 125 kW/kg, about 35 kW/kg to about 140 kW/kg, about 55 kW/kg toabout 75 kW/kg, about 55 kW/kg to about 95 kW/kg, about 55 kW/kg toabout 110 kW/kg, about 55 kW/kg to about 125 kW/kg, about 55 kW/kg toabout 140 kW/kg, about 75 kW/kg to about 95 kW/kg, about 75 kW/kg toabout 110 kW/kg, about 75 kW/kg to about 125 kW/kg, about 75 kW/kg toabout 140 kW/kg, about 95 kW/kg to about 110 kW/kg, about 95 kW/kg toabout 125 kW/kg, about 95 kW/kg to about 140 kW/kg, about 110 kW/kg toabout 125 kW/kg, about 110 kW/kg to about 140 kW/kg or about 125 kW/kgto about 140 kW/kg.

In some embodiments the graphene oxide film has a volumetric powerdensity of at least about 30 kW/L. In some embodiments, the grapheneoxide film has a volumetric power density of at most about 140 kW/L. Insome embodiments, the graphene oxide film has a volumetric power densityof about 30 kW/L to about 140 kW/L. In some embodiments the grapheneoxide film has a volumetric power density of about 30 kW/L to about 50kW/L, about 30 kW/L to about 70 kW/L, about 30 kW/L to about 90 kW/L,about 30 kW/L to about 110 kW/L, about 30 kW/L to about 130 kW/L, about30 kW/L to about 140 kW/L, about 50 kW/L to about 70 kW/L, about 50 kW/Lto about 90 kW/L, about 50 kW/L to about 110 kW/L, about 50 kW/L toabout 130 kW/L, about 50 kW/L to about 140 kW/L, about 70 kW/L to about90 kW/L, about 70 kW/L to about 110 kW/L, about 70 kW/L to about 130kW/L, about 70 kW/L to about 140 kW/L, about 90 kW/L to about 110 kW/L,about 90 kW/L to about 130 kW/L, about 90 kW/L to about 140 kW/L, about110 kW/L to about 130 kW/L, about 110 kW/L to about 140 kW/L or about130 kW/L to about 140 kW/L.

Another aspect provided herein is an electrode comprising a reducedgraphene oxide film, wherein the graphene oxide film contains athree-dimensional hierarchy of pores, wherein the graphene oxide filmhas a thickness of about 6 μm to about 16 μm.

In some embodiments the graphene oxide film has a double layercapacitance of at least about 25 μF/cm². In some embodiments, thegraphene oxide film has a double layer capacitance of at most about 100μF/cm². In some embodiments, the graphene oxide film has a double layercapacitance of about 25 μF/cm² to about 100 μF/cm². In some embodimentsthe graphene oxide film has a double layer capacitance of about 25μF/cm² to about 45 μF/cm², about 25 μF/cm² to about 65 μF/cm², about 25μF/cm² to about 85 μF/cm², about 25 μF/cm² to about 100 μF/cm², about 45μF/cm² to about 65 μF/cm², about 45 μF/cm² to about 85 μF/cm², about 45μF/cm² to about 100 μF/cm², about 65 μF/cm² to about 85 μF/cm², about 65μF/cm² to about 100 μF/cm² or about 85 μF/cm² to about 100 μF/cm².

In some embodiments the graphene oxide film has a characteristic timeconstant o at least about 9 seconds. In some embodiments, the grapheneoxide film has a characteristic time constant o at most about 36seconds. In some embodiments, the graphene oxide film has acharacteristic time constant o about 9 seconds to about 36 seconds. Insome embodiments the graphene oxide film has a characteristic timeconstant o about 9 seconds to about 12 seconds, about 9 seconds to about15 seconds, about 9 seconds to about 18 seconds, about 9 seconds toabout 21 seconds, about 9 seconds to about 24 seconds, about 9 secondsto about 27 seconds, about 9 seconds to about 30 seconds, about 9seconds to about 33 seconds, about 9 seconds to about 36 seconds, about12 seconds to about 15 seconds, about 12 seconds to about 18 seconds,about 12 seconds to about 21 seconds, about 12 seconds to about 24seconds, about 12 seconds to about 27 seconds, about 12 seconds to about30 seconds, about 12 seconds to about 33 seconds, about 12 seconds toabout 36 seconds, about 15 seconds to about 18 seconds, about 15 secondsto about 21 seconds, about 15 seconds to about 24 seconds, about 15seconds to about 27 seconds, about 15 seconds to about 30 seconds, about15 seconds to about 33 seconds, about 15 seconds to about 36 seconds,about 18 seconds to about 21 seconds, about 18 seconds to about 24seconds, about 18 seconds to about 27 seconds, about 18 seconds to about30 seconds, about 18 seconds to about 33 seconds, about 18 seconds toabout 36 seconds, about 21 seconds to about 24 seconds, about 21 secondsto about 27 seconds, about 21 seconds to about 30 seconds, about 21seconds to about 33 seconds, about 21 seconds to about 36 seconds, about24 seconds to about 27 seconds, about 24 seconds to about 30 seconds,about 24 seconds to about 33 seconds, about 24 seconds to about 36seconds, about 27 seconds to about 30 seconds, about 27 seconds to about33 seconds, about 27 seconds to about 36 seconds, about 30 seconds toabout 33 seconds, about 30 seconds to about 36 seconds or about 33seconds to about 36 seconds.

In some embodiments the graphene oxide film has a sheet resistance of atleast about 0.1Ω. In some embodiments, the graphene oxide film has asheet resistance of at most about 0.4Ω. In some embodiments, thegraphene oxide film has a sheet resistance of about 0.1Ω to about 0.4Ω.In some embodiments the graphene oxide film has a sheet resistance ofabout 0.1Ω to about 0.2Ω, about 0.1Ω to about 0.3Ω, about 0.1Ω to about0.4Ω, about 0.2Ω to about 0.3Ω, about 0.2Ω to about 0.4Ω or about 0.3Ωto about 0.4Ω.

In some embodiments the graphene oxide film has a charge transportresistance of at least about 0.1Ω. In some embodiments, the grapheneoxide film has a charge transport resistance of at most about 0.4Ω. Insome embodiments, the graphene oxide film has a charge transportresistance of about 0.1Ω to about 0.4Ω. In some embodiments the grapheneoxide film has a charge transport resistance of about 0.1Ω to about0.2Ω, about 0.1Ω to about 0.3Ω, about 0.1Ω to about 0.4Ω, about 0.2Ω toabout 0.3Ω, about 0.2Ω to about 0.4Ω or about 0.3Ω to about 0.4Ω. Ω

In some embodiments the graphene oxide film has a leak resistance of atleast about 13 kΩ. In some embodiments, the graphene oxide film has aleak resistance of at most about 60 kΩ. In some embodiments, thegraphene oxide film has a leak resistance of about 13 kΩ to about 60 kΩ.In some embodiments the graphene oxide film has a leak resistance ofabout 13 kΩ to about 15 kΩ, about 13 kΩ to about 20 kΩ, about 13 kΩ toabout 30 kΩ, about 13 kΩ to about 40 kΩ, about 13 kΩ to about 50 kΩ,about 13kΩ to about 60 kΩ, about 15kΩ to about 20 kΩ, about 15 kΩ toabout 30 kΩ, about 15 kΩ to about 40 kΩ, about 15kΩ to about 50 kΩ,about 15kΩ to about 60 kΩ, about 20kΩ to about 30 kΩ, about 20kΩ toabout 40 kΩ, about 20kΩ to about 50 kΩ, about 20 kΩ to about 60 kΩ,about 30kΩ to about 40 kΩ, about 30kΩ to about 50 kΩ, about 30kΩ toabout 60 kΩ, about 40kΩ to about 50 kΩ, about 40 kΩ to about 60kΩ orabout 50kΩ to about 60 kΩ.

In some embodiments the graphene oxide film has a Warburg coefficient ofat least about 50 SΩ^(−n). In some embodiments, the graphene oxide filmhas a Warburg coefficient of at most about 200 SΩ^(−n). In someembodiments, the graphene oxide film has a Warburg coefficient of about50 EIS^(−n) to about 200 SΩ^(−n). In some embodiments the graphene oxidefilm has a Warburg coefficient of about 50 SΩ^(−n) to about 75 SΩ^(−n),about 50 SΩ^(−n) to about 100 SΩ^(−n), about 50 SΩ^(−n) to about 125SΩ^(−n), about 50 SΩ^(−n) to about 150 SΩ^(−n), about 50 SΩ^(−n) toabout 175 SΩ^(−n), about 50 SΩ^(−n) to about 200 SΩ^(−n), about 75SΩ^(−n) to about 100 SΩ^(−n), about 75 SΩ^(−n) to about 125 SΩ^(−n),about 75 SΩ^(−n) to about 150 SΩ^(−n), about 75 SΩ^(−n) to about 175SΩ^(−n), about 75 SΩ^(−n) to about 200 SΩ^(−n), about 100 SΩ^(−n) toabout 125 SZS^(−n), about 100 SΩ^(−n)to about 150 SΩ^(−n), about 100SΩ^(−n) to about 175 SΩ^(−n), about 100 SΩ^(−n) to about 200 SΩ^(−n),about 125 SΩ^(−n) to about 150 SΩ^(−n), about 125 SΩ^(−n) to about 175SΩ^(−n), about 125 SΩ^(−n) to about 200 SΩ^(−n), about 150 SΩ^(−n) toabout 175 SΩ^(−n), about 150 SZS^(−n) to about 200 SZS^(−n) or about 175SΩ^(−n) to about 200 SΩ^(−n).

In some embodiments the graphene oxide film has a constant phase elementexponent of at least about 0.2. In some embodiments, the graphene oxidefilm has a constant phase element exponent of at most about 0.8. In someembodiments, the graphene oxide film has a constant phase elementexponent of about 0.2 to about 0.8. In some embodiments the grapheneoxide film has a constant phase element exponent of about 0.2 to about0.3, about 0.2 to about 0.4, about 0.2 to about 0.5, about 0.2 to about0.6, about 0.2 to about 0.7, about 0.2 to about 0.8, about 0.3 to about0.4, about 0.3 to about 0.5, about 0.3 to about 0.6, about 0.3 to about0.7, about 0.3 to about 0.8, about 0.4 to about 0.5, about 0.4 to about0.6, about 0.4 to about 0.7, about 0.4 to about 0.8, about 0.5 to about0.6, about 0.5 to about 0.7, about 0.5 to about 0.8, about 0.6 to about0.7, about 0.6 to about 0.8 or about 0.7 to about 0.8.

In some embodiments the graphene oxide film has a feedback capacitanceof at least about 100 F/g. In some embodiments, the graphene oxide filmhas a feedback capacitance of at most about 400 F/g. In someembodiments, the graphene oxide film has a feedback capacitance of about100 F/g to about 400 F/g. In some embodiments the graphene oxide filmhas a feedback capacitance of about 100 F/g to about 200 F/g, about 100F/g to about 300 F/g, about 100 F/g to about 400 F/g, about 200 F/g toabout 300 F/g, about 200 F/g to about 400 F/g or about 300 F/g to about400 F/g.

In some embodiments the graphene oxide film has a conductivity of atleast about 1,000 S/m. In some embodiments, the graphene oxide film hasa conductivity of at most about 4,000 S/m. In some embodiments, thegraphene oxide film has a conductivity of about 1,000 S/m to about 4,000S/m. In some embodiments the graphene oxide film has a conductivity ofabout 1,000 S/m to about 2,000 S/m, about 1,000 S/m to about 3,000 S/m,about 1,000 S/m to about 4,000 S/m, about 2,000 S/m to about 3,000 S/m,about 2,000 S/m to about 4,000 S/m or about 3,000 S/m to about 4,000S/m.

In some embodiments the graphene oxide film has a strain of at leastabout 3%. In some embodiments, the graphene oxide film has a strain ofat most about 16%. In some embodiments, the graphene oxide film has astrain of about 3% to about 16%. In some embodiments the graphene oxidefilm has a strain of about 3% to about 5%, about 3% to about 7%, about3% to about 9%, about 3% to about 11%, about 3% to about 13%, about 3%to about 16%, about 5% to about 7%, about 5% to about 9%, about 5% toabout 11%, about 5% to about 13%, about 5% to about 16%, about 7% toabout 9%, about 7% to about 11%, about 7% to about 13%, about 7% toabout 16%, about 9% to about 11%, about 9% to about 13%, about 9% toabout 16%, about 11% to about 13%, about 11% to about 16% or about 13%to about 16%.

In some embodiments the graphene oxide film has a tensile strength of atleast about 9 MPa. In some embodiments, the graphene oxide film has atensile strength of at most about 36 MPa. In some embodiments, thegraphene oxide film has a tensile strength of about 9 MPa to about 36MPa. In some embodiments the graphene oxide film has a tensile strengthof about 9 MPa to about 12 MPa, about 9 MPa to about 15 MPa, about 9 MPato about 18 MPa, about 9 MPa to about 21 MPa, about 9 MPa to about 24MPa, about 9 MPa to about 27 MPa, about 9 MPa to about 30 MPa, about 9MPa to about 33 MPa, about 9 MPa to about 36 MPa, about 12 MPa to about15 MPa, about 12 MPa to about 18 MPa, about 12 MPa to about 21 MPa,about 12 MPa to about 24 MPa, about 12 MPa to about 27 MPa, about 12 MPato about 30 MPa, about 12 MPa to about 33 MPa, about 12 MPa to about 36MPa, about 15 MPa to about 18 MPa, about 15 MPa to about 21 MPa, about15 MPa to about 24 MPa, about 15 MPa to about 27 MPa, about 15 MPa toabout 30 MPa, about 15 MPa to about 33 MPa, about 15 MPa to about 36MPa, about 18 MPa to about 21 MPa, about 18 MPa to about 24 MPa, about18 MPa to about 27 MPa, about 18 MPa to about 30 MPa, about 18 MPa toabout 33 MPa, about 18 MPa to about 36 MPa, about 21 MPa to about 24MPa, about 21 MPa to about 27 MPa, about 21 MPa to about 30 MPa, about21 MPa to about 33 MPa, about 21 MPa to about 36 MPa, about 24 MPa toabout 27 MPa, about 24 MPa to about 30 MPa, about 24 MPa to about 33MPa, about 24 MPa to about 36 MPa, about 27 MPa to about 30 MPa, about27 MPa to about 33 MPa, about 27 MPa to about 36 MPa, about 30 MPa toabout 33 MPa, about 30 MPa to about 36 MPa or about 33 MPa to about 36MPa.

In some embodiments the graphene oxide film has a pore size of at leastabout 100 nm. In some embodiments, the graphene oxide film has a poresize of at most about 10,000 nm. In some embodiments, the graphene oxidefilm has a pore size of about 100 nm to about 10,000 nm. In someembodiments the graphene oxide film has a pore size of about 100 nm toabout 200 nm, about 100 nm to about 500 nm, about 100 nm to about 1,000nm, about 100 nm to about 2,000 nm, about 100 nm to about 5,000 nm,about 100 nm to about 10,000 nm, about 200 nm to about 500 nm, about 200nm to about 1,000 nm, about 200 nm to about 2,000 nm, about 200 nm toabout 5,000 nm, about 200 nm to about 10,000 nm, about 500 nm to about1,000 nm, about 500 nm to about 2,000 nm, about 500 nm to about 5,000nm, about 500 nm to about 10,000 nm, about 1,000 nm to about 2,000 nm,about 1,000 nm to about 5,000 nm, about 1,000 nm to about 10,000 nm,about 2,000 nm to about 5,000 nm, about 2,000 nm to about 10,000 nm orabout 5,000 nm to about 10,000 nm.

In some embodiments the graphene oxide film has an areal mass loading ofat least about 0.1 mg/cm². In some embodiments, the graphene oxide filmhas an areal mass loading of at most about 0.4 mg/cm². In someembodiments, the graphene oxide film has an areal mass loading of about0.1 mg/cm² to about 0.4 mg/cm². In some embodiments the graphene oxidefilm has an areal mass loading of about 0.1 mg/cm² to about 0.2 mg/cm²,about 0.1 mg/cm² to about 0.3 mg/cm², about 0.1 mg/cm² to about 0.4mg/cm², about 0.2 mg/cm² to about 0.3 mg/cm², about 0.2 mg/cm² to about0.4 mg/cm² or about 0.3 mg/cm² to about 0.4 mg/cm².

In some embodiments the graphene oxide film has an active density of atleast about 0.08 g/cm². In some embodiments, the graphene oxide film hasan active density of at most about 0.4 g/cm². In some embodiments, thegraphene oxide film has an active density of about 0.08 g/cm² to about0.4 g/cm². In some embodiments the graphene oxide film has an activedensity of about 0.08 g/cm² to about 0.1 g/cm², about 0.08 g/cm² toabout 0.2 g/cm², about 0.08 g/cm² to about 0.3 g/cm², about 0.08 g/cm²to about 0.4 g/cm², about 0.1 g/cm² to about 0.2 g/cm², about 0.1 g/cm²to about 0.3 g/cm², about 0.1 g/cm² to about 0.4 g/cm², about 0.2 g/cm²to about 0.3 g/cm², about 0.2 g/cm² to about 0.4 g/cm² or about 0.3g/cm² to about 0.4 g/cm².

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at least about 140F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at most about 600F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of about 140 F/g toabout 600 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 1 A/g, of about140 F/g to about 200 F/g, about 140 F/g to about 300 F/g, about 140 F/gto about 400 F/g, about 140 F/g to about 500 F/g, about 140 F/g to about600 F/g, about 200 F/g to about 300 F/g, about 200 F/g to about 400 F/g,about 200 F/g to about 500 F/g, about 200 F/g to about 600 F/g, about300 F/g to about 400 F/g, about 300 F/g to about 500 F/g, about 300 F/gto about 600 F/g, about 400 F/g to about 500 F/g, about 400 F/g to about600 F/g or about 500 F/g to about 600 F/g.

In some embodiments the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at least about 20F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at most about 90F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of about 20 F/cm³ toabout 90 F/cm³. In some embodiments the graphene oxide film has avolumetric capacitance, in a current density of about 1 A/g, of about 20F/cm³ to about 30 F/cm³, about 20 F/cm³ to about 40 F/cm³, about 20F/cm³ to about 50 F/cm³, about 20 F/cm³ to about 60 F/cm³, about 20F/cm³ to about 70 F/cm³, about 20 F/cm³ to about 80 F/cm³, about 20F/cm³ to about 90 F/cm³, about 30 F/cm³ to about 40 F/cm³, about 30F/cm³ to about 50 F/cm³, about 30 F/cm³ to about 60 F/cm³, about 30F/cm³ to about 70 F/cm³, about 30 F/cm³ to about 80 F/cm³, about 30F/cm³ to about 90 F/cm³, about 40 F/cm³ to about 50 F/cm³, about 40F/cm³ to about 60 F/cm³, about 40 F/cm³ to about 70 F/cm³, about 40F/cm³ to about 80 F/cm³, about 40 F/cm³ to about 90 F/cm³, about 50F/cm³ to about 60 F/cm³, about 50 F/cm³ to about 70 F/cm³, about 50F/cm³ to about 80 F/cm³, about 50 F/cm³ to about 90 F/cm³, about 60F/cm³ to about 70 F/cm³, about 60 F/cm³ to about 80 F/cm³, about 60F/cm³ to about 90 F/cm³, about 70 F/cm³ to about 80 F/cm³, about 70F/cm³ to about 90 F/cm³ or about 80 F/cm³ to about 90 F/cm3.

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of at least about 90F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of at most about 360F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 500 A/g, of about 90 F/g toabout 360 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 500 A/g, of about90 F/g to about 120 F/g, about 90 F/g to about 150 F/g, about 90 F/g toabout 180 F/g, about 90 F/g to about 210 F/g, about 90 F/g to about 240F/g, about 90 F/g to about 270 F/g, about 90 F/g to about 300 F/g, about90 F/g to about 330 F/g, about 90 F/g to about 360 F/g, about 120 F/g toabout 150 F/g, about 120 F/g to about 180 F/g, about 120 F/g to about210 F/g, about 120 F/g to about 240 F/g, about 120 F/g to about 270 F/g,about 120 F/g to about 300 F/g, about 120 F/g to about 330 F/g, about120 F/g to about 360 F/g, about 150 F/g to about 180 F/g, about 150 F/gto about 210 F/g, about 150 F/g to about 240 F/g, about 150 F/g to about270 F/g, about 150 F/g to about 300 F/g, about 150 F/g to about 330 F/g,about 150 F/g to about 360 F/g, about 180 F/g to about 210 F/g, about180 F/g to about 240 F/g, about 180 F/g to about 270 F/g, about 180 F/gto about 300 F/g, about 180 F/g to about 330 F/g, about 180 F/g to about360 F/g, about 210 F/g to about 240 F/g, about 210 F/g to about 270 F/g,about 210 F/g to about 300 F/g, about 210 F/g to about 330 F/g, about210 F/g to about 360 F/g, about 240 F/g to about 270 F/g, about 240 F/gto about 300 F/g, about 240 F/g to about 330 F/g, about 240 F/g to about360 F/g, about 270 F/g to about 300 F/g, about 270 F/g to about 330 F/g,about 270 F/g to about 360 F/g, about 300 F/g to about 330 F/g, about300 F/g to about 360 F/g or about 330 F/g to about 360 F/g.

In some embodiments the graphene oxide film has a capacitive retention,after about 1000 cycles of charging, of at least about 50%. In someembodiments, the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of at most about 99%. In someembodiments, the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of about 50% to about 99%. In someembodiments the graphene oxide film has a capacitive retention, afterabout 1000 cycles of charging, of about 50% to about 60%, about 50% toabout 70%, about 50% to about 80%, about 50% to about 90%, about 50% toabout 99%, about 60% to about 70%, about 60% to about 80%, about 60% toabout 90%, about 60% to about 99%, about 70% to about 80%, about 70% toabout 90%, about 70% to about 99%, about 80% to about 90%, about 80% toabout 99%, about 90% to about 99%.

In some embodiments the graphene oxide film has a gravimetric energydensity of at least about 4 Wh/kg. In some embodiments, the grapheneoxide film has a gravimetric energy density of at most about 20 Wh/kg.In some embodiments, the graphene oxide film has a gravimetric energydensity of about 4 Wh/kg to about 20 Wh/kg. In some embodiments thegraphene oxide film has a gravimetric energy density of about 4 Wh/kg toabout 6 Wh/kg, about 4 Wh/kg to about 8 Wh/kg, about 4 Wh/kg to about 10Wh/kg, about 4 Wh/kg to about 12 Wh/kg, about 4 Wh/kg to about 14 Wh/kg,about 4 Wh/kg to about 16 Wh/kg, about 4 Wh/kg to about 18 Wh/kg, about4 Wh/kg to about 20 Wh/kg, about 6 Wh/kg to about 8 Wh/kg, about 6 Wh/kgto about 10 Wh/kg, about 6 Wh/kg to about 12 Wh/kg, about 6 Wh/kg toabout 14 Wh/kg, about 6 Wh/kg to about 16 Wh/kg, about 6 Wh/kg to about18 Wh/kg, about 6 Wh/kg to about 20 Wh/kg, about 8 Wh/kg to about 10Wh/kg, about 8 Wh/kg to about 12 Wh/kg, about 8 Wh/kg to about 14 Wh/kg,about 8 Wh/kg to about 16 Wh/kg, about 8 Wh/kg to about 18 Wh/kg, about8 Wh/kg to about 20 Wh/kg, about 10 Wh/kg to about 12 Wh/kg, about 10Wh/kg to about 14 Wh/kg, about 10 Wh/kg to about 16 Wh/kg, about 10Wh/kg to about 18 Wh/kg, about 10 Wh/kg to about 20 Wh/kg, about 12Wh/kg to about 14 Wh/kg, about 12 Wh/kg to about 16 Wh/kg, about 12Wh/kg to about 18 Wh/kg, about 12 Wh/kg to about 20 Wh/kg, about 14Wh/kg to about 16 Wh/kg, about 14 Wh/kg to about 18 Wh/kg, about 14Wh/kg to about 20 Wh/kg, about 16 Wh/kg to about 18 Wh/kg, about 16Wh/kg to about 20 Wh/kg, or about 18 Wh/kg to about 20 Wh/kg.

In some embodiments the graphene oxide film has a volumetric energydensity of at least about 0.75 Wh/L. In some embodiments, the grapheneoxide film has a volumetric energy density of at most about 3 Wh/L. Insome embodiments, the graphene oxide film has a volumetric energydensity of about 0.75 Wh/L to about 3 Wh/L. In some embodiments thegraphene oxide film has a volumetric energy density of about 0.75 Wh/Lto about 1 Wh/L, about 0.75 Wh/L to about 1.25 Wh/L, about 0.75 Wh/L toabout 1.5 Wh/L, about 0.75 Wh/L to about 1.75 Wh/L, about 0.75 Wh/L toabout 2 Wh/L, about 0.75 Wh/L to about 2.25 Wh/L, about 0.75 Wh/L toabout 2.5 Wh/L, about 0.75 Wh/L to about 2.75 Wh/L, about 0.75 Wh/L toabout 3 Wh/L, about 1 Wh/L to about 1.25 Wh/L, about 1 Wh/L to about 1.5Wh/L, about 1 Wh/L to about 1.75 Wh/L, about 1 Wh/L to about 2 Wh/L,about 1 Wh/L to about 2.25 Wh/L, about 1 Wh/L to about 2.5 Wh/L, about 1Wh/L to about 2.75 Wh/L, about 1 Wh/L to about 3 Wh/L, about 1.25 Wh/Lto about 1.5 Wh/L, about 1.25 Wh/L to about 1.75 Wh/L, about 1.25 Wh/Lto about 2 Wh/L, about 1.25 Wh/L to about 2.25 Wh/L, about 1.25 Wh/L toabout 2.5 Wh/L, about 1.25 Wh/L to about 2.75 Wh/L, about 1.25 Wh/L toabout 3 Wh/L, about 1.5 Wh/L to about 1.75 Wh/L, about 1.5 Wh/L to about2 Wh/L, about 1.5 Wh/L to about 2.25 Wh/L, about 1.5 Wh/L to about 2.5Wh/L, about 1.5 Wh/L to about 2.75 Wh/L, about 1.5 Wh/L to about 3 Wh/L,about 1.75 Wh/L to about 2 Wh/L, about 1.75 Wh/L to about 2.25 Wh/L,about 1.75 Wh/L to about 2.5 Wh/L, about 1.75 Wh/L to about 2.75 Wh/L,about 1.75 Wh/L to about 3 Wh/L, about 2 Wh/L to about 2.25 Wh/L, about2 Wh/L to about 2.5 Wh/L, about 2 Wh/L to about 2.75 Wh/L, about 2 Wh/Lto about 3 Wh/L, about 2.25 Wh/L to about 2.5 Wh/L, about 2.25 Wh/L toabout 2.75 Wh/L, about 2.25 Wh/L to about 3 Wh/L, about 2.5 Wh/L toabout 2.75 Wh/L, about 2.5 Wh/L to about 3 Wh/L or about 2.75 Wh/L toabout 3 Wh/L.

In some embodiments the graphene oxide film has a gravimetric powerdensity of at least about 140 kW/kg. In some embodiments, the grapheneoxide film has a gravimetric power density of at most about 600 kW/kg.In some embodiments, the graphene oxide film has a gravimetric powerdensity of about 140 kW/kg to about 600 kW/kg. In some embodiments thegraphene oxide film has a gravimetric power density of about 140 kW/kgto about 200 kW/kg, about 140 kW/kg to about 260 kW/kg, about 140 kW/kgto about 320 kW/kg, about 140 kW/kg to about 380 kW/kg, about 140 kW/kgto about 440 kW/kg, about 140 kW/kg to about 500 kW/kg, about 140 kW/kgto about 560 kW/kg, about 140 kW/kg to about 600 kW/kg, about 200 kW/kgto about 260 kW/kg, about 200 kW/kg to about 320 kW/kg, about 200 kW/kgto about 380 kW/kg, about 200 kW/kg to about 440 kW/kg, about 200 kW/kgto about 500 kW/kg, about 200 kW/kg to about 560 kW/kg, about 200 kW/kgto about 600 kW/kg, about 260 kW/kg to about 320 kW/kg, about 260 kW/kgto about 380 kW/kg, about 260 kW/kg to about 440 kW/kg, about 260 kW/kgto about 500 kW/kg, about 260 kW/kg to about 560 kW/kg, about 260 kW/kgto about 600 kW/kg, about 320 kW/kg to about 380 kW/kg, about 320 kW/kgto about 440 kW/kg, about 320 kW/kg to about 500 kW/kg, about 320 kW/kgto about 560 kW/kg, about 320 kW/kg to about 600 kW/kg, about 380 kW/kgto about 440 kW/kg, about 380 kW/kg to about 500 kW/kg, about 380 kW/kgto about 560 kW/kg, about 380 kW/kg to about 600 kW/kg, about 440 kW/kgto about 500 kW/kg, about 440 kW/kg to about 560 kW/kg, about 440 kW/kgto about 600 kW/kg, about 500 kW/kg to about 560 kW/kg, about 500 kW/kgto about 600 kW/kg or about 560 kW/kg to about 600 kW/kg.

In some embodiments the graphene oxide film has a volumetric powerdensity of at least about 25 kW/L. In some embodiments, the grapheneoxide film has a volumetric power density of at most about 100 kW/L. Insome embodiments, the graphene oxide film has a volumetric power densityof about 25 kW/L to about 100 kW/L. In some embodiments the grapheneoxide film has a volumetric power density of about 25 kW/L to about 50kW/L, about 25 kW/L to about 75 kW/L, about 25 kW/L to about 100 kW/L,about 50 kW/L to about 75 kW/L, about 50 kW/L to about 100 kW/L or about75 kW/L to about 100 kW/L.

In some embodiments the graphene oxide film has an areal capacitance ofat least about 25 mF/cm². In some embodiments, the graphene oxide filmhas an areal capacitance of at most about 100 mF/cm². In someembodiments, the graphene oxide film has an areal capacitance of about25 mF/cm² to about 100 mF/cm². In some embodiments the graphene oxidefilm has an areal capacitance of about 25 mF/cm² to about 50 mF/cm²,about 25 mF/cm² to about 75 mF/cm², about 25 mF/cm² to about 100 mF/cm²,about 50 mF/cm² to about 75 mF/cm², about 50 mF/cm² to about 100 mF/cm²or about 75 mF/cm² to about 100 mF/cm².

Another aspect provided herein is an electrode comprising a reducedgraphene oxide film, wherein the graphene oxide film contains athree-dimensional hierarchy of pores, wherein the graphene oxide filmhas a thickness of about 15 μm to about 32 μm.

In some embodiments the graphene oxide film has an areal mass loading ofat least about 0.2 mg/cm². In some embodiments, the graphene oxide filmhas an areal mass loading of at most about 0.8 mg/cm². In someembodiments, the graphene oxide film has an areal mass loading of about0.2 mg/cm² to about 0.8 mg/cm². In some embodiments the graphene oxidefilm has an areal mass loading of about 0.2 mg/cm² to about 0.4 mg/cm²,about 0.2 mg/cm² to about 0.6 mg/cm², about 0.2 mg/cm² to about 0.8mg/cm², about 0.4 mg/cm² to about 0.6 mg/cm², about 0.4 mg/cm² to about0.8 mg/cm² or about 0.6 mg/cm² to about 0.8 mg/cm².

In some embodiments the graphene oxide film has an active density of atleast about 0.1 g/cm³. In some embodiments, the graphene oxide film hasan active density of at most about 0.5 g/cm³. In some embodiments, thegraphene oxide film has an active density of about 0.1 g/cm³ to about0.5 g/cm³. In some embodiments the graphene oxide film has an activedensity of about 0.1 g/cm³ to about 0.2 g/cm³, about 0.1 g/cm³ to about0.3 g/cm³, about 0.1 g/cm³ to about 0.4 g/cm³, about 0.1 g/cm³ to about0.5 g/cm³, about 0.2 g/cm³ to about 0.3 g/cm³, about 0.2 g/cm³ to about0.4 g/cm³, about 0.2 g/cm³ to about 0.5 g/cm³, about 0.3 g/cm³ to about0.4 g/cm³, about 0.3 g/cm³ to about 0.5 g/cm³ or about 0.4 g/cm³ toabout 0.5 g/cm³.

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at least about 130F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at most about 550F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of about 130 F/g toabout 550 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 1 A/g, of about130 F/g to about 150 F/g, about 130 F/g to about 200 F/g, about 130 F/gto about 250 F/g, about 130 F/g to about 300 F/g, about 130 F/g to about350 F/g, about 130 F/g to about 400 F/g, about 130 F/g to about 450 F/g,about 130 F/g to about 500 F/g, about 130 F/g to about 550 F/g, about150 F/g to about 200 F/g, about 150 F/g to about 250 F/g, about 150 F/gto about 300 F/g, about 150 F/g to about 350 F/g, about 150 F/g to about400 F/g, about 150 F/g to about 450 F/g, about 150 F/g to about 500 F/g,about 150 F/g to about 550 F/g, about 200 F/g to about 250 F/g, about200 F/g to about 300 F/g, about 200 F/g to about 350 F/g, about 200 F/gto about 400 F/g, about 200 F/g to about 450 F/g, about 200 F/g to about500 F/g, about 200 F/g to about 550 F/g, about 250 F/g to about 300 F/g,about 250 F/g to about 350 F/g, about 250 F/g to about 400 F/g, about250 F/g to about 450 F/g, about 250 F/g to about 500 F/g, about 250 F/gto about 550 F/g, about 300 F/g to about 350 F/g, about 300 F/g to about400 F/g, about 300 F/g to about 450 F/g, about 300 F/g to about 500 F/g,about 300 F/g to about 550 F/g, about 350 F/g to about 400 F/g, about350 F/g to about 450 F/g, about 350 F/g to about 500 F/g, about 350 F/gto about 550 F/g, about 400 F/g to about 450 F/g, about 400 F/g to about500 F/g, about 400 F/g to about 550 F/g, about 450 F/g to about 500 F/g,about 450 F/g to about 550 F/g or about 500 F/g to about 550 F/g.

In some embodiments the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at least about 20F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at most about 100F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of about 20 F/cm³ toabout 100 F/cm³. In some embodiments the graphene oxide film has avolumetric capacitance, in a current density of about 1 A/g, of about 20F/cm³ to about 40 F/cm³, about 20 F/cm³ to about 60 F/cm³, about 20F/cm³ to about 80 F/cm³, about 20 F/cm³ to about 100 F/cm³, about 40F/cm³ to about 60 F/cm³, about 40 F/cm³ to about 80 F/cm³, about 40F/cm³ to about 100 F/cm³, about 60 F/cm³ to about 80 F/cm³, about 60F/cm³ to about 100 F/cm³ or about 80 F/cm³ to about 100 F/cm³.

In some embodiments the graphene oxide film has a gravimetric energydensity of at least about 4 Wh/kg. In some embodiments, the grapheneoxide film has a gravimetric energy density of at most about 20 Wh/kg.In some embodiments, the graphene oxide film has a gravimetric energydensity of about 4 Wh/kg to about 20 Wh/kg. In some embodiments thegraphene oxide film has a gravimetric energy density of about 4 Wh/kg toabout 8 Wh/kg, about 4 Wh/kg to about 12 Wh/kg, about 4 Wh/kg to about16 Wh/kg, about 4 Wh/kg to about 20 Wh/kg, about 8 Wh/kg to about 12Wh/kg, about 8 Wh/kg to about 16 Wh/kg, about 8 Wh/kg to about 20 Wh/kg,about 12 Wh/kg to about 16 Wh/kg, about 12 Wh/kg to about 20 Wh/kg orabout 16 Wh/kg to about 20 Wh/kg.

In some embodiments the graphene oxide film has a volumetric energydensity of at least about 0.75 Wh/L. In some embodiments, the grapheneoxide film has a volumetric energy density of at most about 3 Wh/L. Insome embodiments, the graphene oxide film has a volumetric energydensity of about 0.75 Wh/L to about 3 Wh/L. In some embodiments thegraphene oxide film has a volumetric energy density of about 0.75 Wh/Lto about 1 Wh/L, about 0.75 Wh/L to about 1.5 Wh/L, about 0.75 Wh/L toabout 2 Wh/L, about 0.75 Wh/L to about 2.5 Wh/L, about 0.75 Wh/L toabout 3 Wh/L, about 1 Wh/L to about 1.5 Wh/L, about 1 Wh/L to about 2Wh/L, about 1 Wh/L to about 2.5 Wh/L, about 1 Wh/L to about 3 Wh/L,about 1.5 Wh/L to about 2 Wh/L, about 1.5 Wh/L to about 2.5 Wh/L, about1.5 Wh/L to about 3 Wh/L, about 2 Wh/L to about 2.5 Wh/L, about 2 Wh/Lto about 3 Wh/L or about 2.5 Wh/L to about 3 Wh/L.

In some embodiments the graphene oxide film has a gravimetric powerdensity of at least about 75 kW/kg. In some embodiments, the grapheneoxide film has a gravimetric power density of at most about 300 kW/kg.In some embodiments, the graphene oxide film has a gravimetric powerdensity of about 75 kW/kg to about 300 kW/kg. In some embodiments thegraphene oxide film has a gravimetric power density of about 75 kW/kg toabout 100 kW/kg, about 75 kW/kg to about 150 kW/kg, about 75 kW/kg toabout 200 kW/kg, about 75 kW/kg to about 250 kW/kg, about 75 kW/kg toabout 300 kW/kg, about 100 kW/kg to about 150 kW/kg, about 100 kW/kg toabout 200 kW/kg, about 100 kW/kg to about 250 kW/kg, about 100 kW/kg toabout 300 kW/kg, about 150 kW/kg to about 200 kW/kg, about 150 kW/kg toabout 250 kW/kg, about 150 kW/kg to about 300 kW/kg, about 200 kW/kg toabout 250 kW/kg, about 200 kW/kg to about 300 kW/kg or about 250 kW/kgto about 300 kW/kg.

In some embodiments the graphene oxide film has a volumetric powerdensity of at least about 14 kW/L. In some embodiments, the grapheneoxide film has a volumetric power density of at most about 60 kW/L. Insome embodiments, the graphene oxide film has a volumetric power densityof about 14 kW/L to about 60 kW/L. In some embodiments the grapheneoxide film has a volumetric power density of about 14 kW/L to about 20kW/L, about 14 kW/L to about 30 kW/L, about 14 kW/L to about 40 kW/L,about 14 kW/L to about 50 kW/L, about 14 kW/L to about 60 kW/L, about 20kW/L to about 30 kW/L, about 20 kW/L to about 40 kW/L, about 20 kW/L toabout 50 kW/L, about 20 kW/L to about 60 kW/L, about 30 kW/L to about 40kW/L, about 30 kW/L to about 50 kW/L, about 30 kW/L to about 60 kW/L,about 40 kW/L to about 50 kW/L, about 40 kW/L to about 60 kW/L or about50 kW/L to about 60 kW/L.

In some embodiments the graphene oxide film has an areal capacitance ofat least about 50 mF/cm². In some embodiments, the graphene oxide filmhas an areal capacitance of at most about 300 mF/cm². In someembodiments, the graphene oxide film has an areal capacitance of about50 mF/cm² to about 300 mF/cm². In some embodiments the graphene oxidefilm has an areal capacitance of about 50 mF/cm² to about 100 mF/cm²,about 50 mF/cm² to about 150 mF/cm², about 50 mF/cm² to about 200mF/cm², about 50 mF/cm² to about 250 mF/cm², about 50 mF/cm² to about300 mF/cm², about 100 mF/cm² to about 150 mF/cm², about 100 mF/cm² toabout 200 mF/cm², about 100 mF/cm ² to about 250 mF/cm², about 100mF/cm² to about 300 mF/cm², about 150 mF/cm² to about 200 mF/cm², about150 mF/cm² to about 250 mF/cm², about 150 mF/cm² to about 300 mF/cm²,about 200 mF/cm² to about 250 mF/cm², about 200 mF/cm² to about 300mF/cm² or about 250 mF/cm² to about 300 mF/cm².

Another aspect provided herein is an electrode comprising a reducedgraphene oxide film, wherein the graphene oxide film contains athree-dimensional hierarchy of pores, wherein the graphene oxide filmhas a thickness of about 32 μm to about 60 μm.

In some embodiments the graphene oxide film has an areal mass loading ofat least about 0.5 mg/cm². In some embodiments, the graphene oxide filmhas an areal mass loading of at most about 3 mg/cm². In someembodiments, the graphene oxide film has an areal mass loading of about0.5 mg/cm² to about 3 mg/cm². In some embodiments the graphene oxidefilm has an areal mass loading of about 0.5 mg/cm² to about 0.75 mg/cm²,about 0.5 mg/cm² to about 1 mg/cm², about 0.5 mg/cm² to about 1.5mg/cm², about 0.5 mg/cm² to about 2 mg/cm², about 0.5 mg/cm² to about2.5 mg/cm², about 0.5 mg/cm² to about 3 mg/cm², about 0.75 mg/cm² toabout 1 mg/cm², about 0.75 mg/cm² to about 1.5 mg/cm², about 0.75 mg/cm²to about 2 mg/cm², about 0.75 mg/cm² to about 2.5 mg/cm², about 0.75mg/cm² to about 3 mg/cm², about 1 mg/cm² to about 1.5 mg/cm², about 1mg/cm² to about 2 mg/cm ², about 1 mg/cm² to about 2.5 mg/cm², about 1mg/cm² to about 3 mg/cm², about 1.5 mg/cm ² to about 2 mg/cm², about 1.5mg/cm² to about 2.5 mg/cm², about 1.5 mg/cm² to about 3 mg/cm ², about 2mg/cm² to about 2.5 mg/cm², about 2 mg/cm² to about 3 mg/cm² or about2.5 mg/cm² to about 3 mg/cm².

In some embodiments the graphene oxide film has an active density of atleast about 0.1 g/cm². In some embodiments, the graphene oxide film hasan active density of at most about 0.5 g/cm². In some embodiments, thegraphene oxide film has an active density of about 0.1 g/cm² to about0.5 g/cm². In some embodiments the graphene oxide film has an activedensity of about 0.1 g/cm² to about 0.2 g/cm², about 0.1 g/cm² to about0.3 g/cm², about 0.1 g/cm² to about 0.4 g/cm², about 0.1 g/cm² to about0.5 g/cm², about 0.2 g/cm² to about 0.3 g/cm², about 0.2 g/cm² to about0.4 g/cm², about 0.2 g/cm² to about 0.5 g/cm², about 0.3 g/cm² to about0.4 g/cm², about 0.3 g/cm² to about 0.5 g/cm² or about 0.4 g/cm² toabout 0.5 g/cm².

In some embodiments the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at least about 120F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of at most about 500F/g. In some embodiments, the graphene oxide film has a gravimetriccapacitance, in a current density of about 1 A/g, of about 120 F/g toabout 500 F/g. In some embodiments the graphene oxide film has agravimetric capacitance, in a current density of about 1 A/g, of about120 F/g to about 150 F/g, about 120 F/g to about 200 F/g, about 120 F/gto about 300 F/g, about 120 F/g to about 400 F/g, about 120 F/g to about500 F/g, about 150 F/g to about 200 F/g, about 150 F/g to about 300 F/g,about 150 F/g to about 400 F/g, about 150 F/g to about 500 F/g, about200 F/g to about 300 F/g, about 200 F/g to about 400 F/g, about 200 F/gto about 500 F/g, about 300 F/g to about 400 F/g, about 300 F/g to about500 F/g or about 400 F/g to about 500 F/g.

In some embodiments the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at least about 20F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of at most about 100F/cm³. In some embodiments, the graphene oxide film has a volumetriccapacitance, in a current density of about 1 A/g, of about 20 F/cm³ toabout 100 F/cm³. In some embodiments the graphene oxide film has avolumetric capacitance, in a current density of about 1 A/g, of about 20F/cm³ to about 30 F/cm³, about 20 F/cm³ to about 40 F/cm³, about 20F/cm³ to about 50 F/cm³, about 20 F/cm³ to about 60 F/cm³, about 20F/cm³ to about 70 F/cm³, about 20 F/cm³ to about 80 F/cm³, about 20F/cm³ to about 90 F/cm³, about 20 F/cm³ to about 100 F/cm³, about 30F/cm³ to about 40 F/cm³, about 30 F/cm³ to about 50 F/cm³, about 30F/cm³ to about 60 F/cm³, about 30 F/cm³ to about 70 F/cm³, about 30F/cm³ to about 80 F/cm³, about 30 F/cm³ to about 90 F/cm³, about 30F/cm³ to about 100 F/cm³, about 40 F/cm³ to about 50 F/cm³, about 40F/cm³ to about 60 F/cm³, about 40 F/cm³ to about 70 F/cm³, about 40F/cm³ to about 80 F/cm³, about 40 F/cm³ to about 90 F/cm³, about 40F/cm³ to about 100 F/cm³, about 50 F/cm³ to about 60 F/cm³, about 50F/cm³ to about 70 F/cm³, about 50 F/cm³ to about 80 F/cm³, about 50F/cm³ to about 90 F/cm³, about 50 F/cm³ to about 100 F/cm³, about 60F/cm³ to about 70 F/cm³, about 60 F/cm³ to about 80 F/cm³, about 60F/cm³ to about 90 F/cm³, about 60 F/cm³ to about 100 F/cm³, about 70F/cm³ to about 80 F/cm³, about 70 F/cm³ to about 90 F/cm³, about 70F/cm³ to about 100 F/cm³, about 80 F/cm³ to about 90 F/cm³, about 80F/cm³ to about 100 F/cm³ or about 90 F/cm³ to about 100 F/cm³.

In some embodiments the graphene oxide film has a gravimetric energydensity of at least about 4 Wh/kg. In some embodiments, the grapheneoxide film has a gravimetric energy density of at most about 18 Wh/kg.In some embodiments, the graphene oxide film has a gravimetric energydensity of about 4 Wh/kg to about 18 Wh/kg. In some embodiments thegraphene oxide film has a gravimetric energy density of about 4 Wh/kg toabout 6 Wh/kg, about 4 Wh/kg to about 8 Wh/kg, about 4 Wh/kg to about 10Wh/kg, about 4 Wh/kg to about 12 Wh/kg, about 4 Wh/kg to about 14 Wh/kg,about 4 Wh/kg to about 16 Wh/kg, about 4 Wh/kg to about 18 Wh/kg, about6 Wh/kg to about 8 Wh/kg, about 6 Wh/kg to about 10 Wh/kg, about 6 Wh/kgto about 12 Wh/kg, about 6 Wh/kg to about 14 Wh/kg, about 6 Wh/kg toabout 16 Wh/kg, about 6 Wh/kg to about 18 Wh/kg, about 8 Wh/kg to about10 Wh/kg, about 8 Wh/kg to about 12 Wh/kg, about 8 Wh/kg to about 14Wh/kg, about 8 Wh/kg to about 16 Wh/kg, about 8 Wh/kg to about 18 Wh/kg,about 10 Wh/kg to about 12 Wh/kg, about 10 Wh/kg to about 14 Wh/kg,about 10 Wh/kg to about 16 Wh/kg, about 10 Wh/kg to about 18 Wh/kg,about 12 Wh/kg to about 14 Wh/kg, about 12 Wh/kg to about 16 Wh/kg,about 12 Wh/kg to about 18 Wh/kg, about 14 Wh/kg to about 16 Wh/kg,about 14 Wh/kg to about 18 Wh/kg or about 16 Wh/kg to about 18 Wh/kg.

In some embodiments the graphene oxide film has a volumetric energydensity of at least about 1 Wh/L. In some embodiments, the grapheneoxide film has a volumetric energy density of at most about 4 Wh/L. Insome embodiments, the graphene oxide film has a volumetric energydensity of about 1 Wh/L to about 4 Wh/L. In some embodiments thegraphene oxide film has a volumetric energy density of about 1 Wh/L toabout 2 Wh/L, about 1 Wh/L to about 3 Wh/L, about 1 Wh/L to about 4Wh/L, about 2 Wh/L to about 3 Wh/L, about 2 Wh/L to about 4 Wh/L orabout 3 Wh/L to about 4 Wh/L.

In some embodiments the graphene oxide film has a gravimetric powerdensity of at least about 25 kW/kg. In some embodiments, the grapheneoxide film has a gravimetric power density of at most about 120 kW/kg.In some embodiments, the graphene oxide film has a gravimetric powerdensity of about 25 kW/kg to about 120 kW/kg. In some embodiments thegraphene oxide film has a gravimetric power density of about 25 kW/kg toabout 50 kW/kg, about 25 kW/kg to about 75 kW/kg, about 25 kW/kg toabout 100 kW/kg, about 25 kW/kg to about 120 kW/kg, about 50 kW/kg toabout 75 kW/kg, about 50 kW/kg to about 100 kW/kg, about 50 kW/kg toabout 120 kW/kg, about 75 kW/kg to about 100 kW/kg, about 75 kW/kg toabout 120 kW/kg or about 100 kW/kg to about 120 kW/kg.

In some embodiments the graphene oxide film has a volumetric powerdensity of at least about 6 kW/L. In some embodiments, the grapheneoxide film has a volumetric power density of at most about 25 kW/L. Insome embodiments, the graphene oxide film has a volumetric power densityof about 6 kW/L to about 25 kW/L. In some embodiments the graphene oxidefilm has a volumetric power density of about 6 kW/L to about 10 kW/L,about 6 kW/L to about 15 kW/L, about 6 kW/L to about 20 kW/L, about 6kW/L to about 25 kW/L, about 10 kW/L to about 15 kW/L, about 10 kW/L toabout 20 kW/L, about 10 kW/L to about 25 kW/L, about 15 kW/L to about 20kW/L, about 15 kW/L to about 25 kW/L or about 20 kW/L to about 25 kW/L.

In some embodiments the graphene oxide film has an areal capacitance ofat least about 125 mF/cm². In some embodiments, the graphene oxide filmhas an areal capacitance of at most about 500 mF/cm². In someembodiments, the graphene oxide film has an areal capacitance of about125 mF/cm² to about 500 mF/cm². In some embodiments the graphene oxidefilm has an areal capacitance of about 125 mF/cm² to about 150 mF/cm²,about 125 mF/cm² to about 200 mF/cm², about 125 mF/cm ² to about 250mF/cm², about 125 mF/cm² to about 300 mF/cm², about 125 mF/cm² to about350 mF/cm², about 125 mF/cm² to about 400 mF/cm², about 125 mF/cm² toabout 450 mF/cm², about 125 mF/cm² to about 500 mF/cm², about 150 mF/cm²to about 200 mF/cm², about 150 mF/cm² to about 250 mF/cm², about 150mF/cm² to about 300 mF/cm², about 150 mF/cm² to about 350 mF/cm², about150 mF/cm² to about 400 mF/cm², about 150 mF/cm² to about 450 mF/cm²,about 150 mF/cm² to about 500 mF/cm², about 200 mF/cm² to about 250mF/cm², about 200 mF/cm ² to about 300 mF/cm², about 200 mF/cm² to about350 mF/cm², about 200 mF/cm² to about 400 mF/cm², about 200 mF/cm² toabout 450 mF/cm², about 200 mF/cm² to about 500 mF/cm², about 250 mF/cm²to about 300 mF/cm², about 250 mF/cm² to about 350 mF/cm², about 250mF/cm² to about 400 mF/cm², about 250 mF/cm² to about 450 mF/cm², about250 mF/cm² to about 500 mF/cm², about 300 mF/cm² to about 350 mF/cm²,about 300 mF/cm² to about 400 mF/cm², about 300 mF/cm² to about 450mF/cm², about 300 mF/cm² to about 500 mF/cm², about 350 mF/cm² to about400 mF/cm², about 350 mF/cm² to about 450 mF/cm², about 350 mF/cm² toabout 500 mF/cm ², about 400 mF/cm² to about 450 mF/cm², about 400mF/cm² to about 500 mF/cm² or about 450 mF/cm² to about 500 mF/cm².

Another aspect provided herein is a superconductor device comprising twoelectrodes, wherein each electrode comprises a reduced graphene oxidefilm, further comprising an electrolyte further comprising a separator,further comprising a housing, further comprising an electrolyte, aseparator, a housing or any combination thereof, wherein the electrolyteis aqueous, wherein the electrolyte comprises an acid, wherein the acidis a strong acid wherein the strong acid comprises perchloric acid,hydroiodic acid, hydrobromic acid, hydrochloric acid, sulfuric acid,p-toluenesulfonic acid methanesulfonic acid, or any combination thereof,wherein the electrolyte has a concentration of at least about 0.5 Mwherein the electrolyte has a concentration of at most about 2 M,wherein the electrolyte has a concentration of about 0.5 M to about 2 M,wherein the separator is placed between the two electrodes wherein theseparator is ion porous, wherein the separator is comprised of apolymer, wherein the separator is comprised of neoprene, nylon,polyvinyl chloride, polystyrene, polyethylene, polypropylene,polyacrylonitrile, PVB, silicone or any combination thereof, wherein thehousing comprises a tape, a film, a bag, a resin, a casing or anycombination thereof, wherein the housing is comprised of polyimide,Kapton, Teflon, plastic, epoxy, glue, cement, mucilage, paste, plastic,wood, carbon fiber, fiberglass, glass, metal or any combination thereof,wherein the electrodes each have a thickness of about 1 μm to about 4μm.

In some embodiments the superconductor has a volumetric energy densityof at least about 0.1 Wh/L. In some embodiments, the superconductor hasa volumetric energy density of at most about 0.4 Wh/L. In someembodiments, the superconductor has a volumetric energy density of about0.1 Wh/L to about 0.4 Wh/L. In some embodiments the superconductor has avolumetric energy density of about 0.1 Wh/L to about 0.2 Wh/L, about 0.1Wh/L to about 0.3 Wh/L, about 0.1 Wh/L to about 0.4 Wh/L, about 0.2 Wh/Lto about 0.3 Wh/L, about 0.2 Wh/L to about 0.4 Wh/L or about 0.3 Wh/L toabout 0.4 Wh/L.

In some embodiments the superconductor has a volumetric power density ofat least about 1 kW/L. In some embodiments, the superconductor has avolumetric power density of at most about 4 kW/L. In some embodiments,the superconductor has a volumetric power density of about 1 kW/L toabout 4 kW/L. In some embodiments the superconductor has a volumetricpower density of about 1 kW/L to about 2 kW/L, about 1 kW/L to about 3kW/L, about 1 kW/L to about 4 kW/L, about 2 kW/L to about 3 kW/L, about2 kW/L to about 4 kW/L or about 3 kW/L to about 4 kW/L.

In some embodiments, the reduced graphene oxide film of thesuperconductor contains a three-dimensional hierarchy of pores.

In some embodiments, the electrodes each have a thickness of about 6 μmto about 16 μm.

In some embodiments the superconductor has a volumetric energy densityof at least about 0.5 Wh/L. In some embodiments, the superconductor hasa volumetric energy density of at most about 2.25 Wh/L. In someembodiments, the superconductor has a volumetric energy density of about0.5 Wh/L to about 2.25 Wh/L. In some embodiments the superconductor hasa volumetric energy density of about 0.5 Wh/L to about 1 Wh/L, about 0.5Wh/L to about 1.5 Wh/L, about 0.5 Wh/L to about 2 Wh/L, about 0.5 Wh/Lto about 2.25 Wh/L, about 1 Wh/L to about 1.5 Wh/L, about 1 Wh/L toabout 2 Wh/L, about 1 Wh/L to about 2.25 Wh/L, about 1.5 Wh/L to about 2Wh/L, about 1.5 Wh/L to about 2.25 Wh/L or about 2 Wh/L to about 2.25Wh/L.

In some embodiments the superconductor has a volumetric power density ofat least about 3 kW/L. In some embodiments, the superconductor has avolumetric power density of at most about 16 kW/L. In some embodiments,the superconductor has a volumetric power density of about 3 kW/L toabout 16 kW/L. In some embodiments the superconductor has a volumetricpower density of about 3 kW/L to about 6 kW/L, about 3 kW/L to about 9kW/L, about 3 kW/L to about 12 kW/L, about 3 kW/L to about 16 kW/L,about 6 kW/L to about 9 kW/L, about 6 kW/L to about 12 kW/L, about 6kW/L to about 16 kW/L, about 9 kW/L to about 12 kW/L, about 9 kW/L toabout 16 kW/L or about 12 kW/L to about 16 kW/L.

In some embodiments, the electrodes each have a thickness of about 16 μmto about 32 μm.

In some embodiments the superconductor has a volumetric energy densityof at least about 0.25 Wh/L. In some embodiments, the superconductor hasa volumetric energy density of at most about 1.5 Wh/L. In someembodiments, the superconductor has a volumetric energy density of about0.25 Wh/L to about 1.5 Wh/L. In some embodiments the superconductor hasa volumetric energy density of about 0.25 Wh/L to about 0.5 Wh/L, about0.25 Wh/L to about 0.75 Wh/L, about 0.25 Wh/L to about 1 Wh/L, about0.25 Wh/L to about 1.25 Wh/L, about 0.25 Wh/L to about 1.5 Wh/L, about0.5 Wh/L to about 0.75 Wh/L, about 0.5 Wh/L to about 1 Wh/L, about 0.5Wh/L to about 1.25 Wh/L, about 0.5 Wh/L to about 1.5 Wh/L, about 0.75Wh/L to about 1 Wh/L, about 0.75 Wh/L to about 1.25 Wh/L, about 0.75Wh/L to about 1.5 Wh/L, about 1 Wh/L to about 1.25 Wh/L, about 1 Wh/L toabout 1.5 Wh/L or about 1.25 Wh/L to about 1.5 Wh/L.

In some embodiments the superconductor has a volumetric power density ofat least about 5 kW/L. In some embodiments, the superconductor has avolumetric power density of at most about 20 kW/L. In some embodiments,the superconductor has a volumetric power density of about 5 kW/L toabout 20 kW/L. In some embodiments the superconductor has a volumetricpower density of about 5 kW/L to about 10 kW/L, about 5 kW/L to about 15kW/L, about 5 kW/L to about 20 kW/L, about 10 kW/L to about 15 kW/L,about 10 kW/L to about 20 kW/L or about 15 kW/L to about 20 kW/L.

In some embodiments, the electrodes each have a thickness of about 32 μmto about 60 μm.

In some embodiments the superconductor has a volumetric energy densityof at least about 0.1 Wh/L. In some embodiments, the superconductor hasa volumetric energy density of at most about 0.5 Wh/L. In someembodiments, the superconductor has a volumetric energy density of about0.1 Wh/L to about 0.5 Wh/L. In some embodiments the superconductor has avolumetric energy density of about 0.1 Wh/L to about 0.2 Wh/L, about 0.1Wh/L to about 0.3 Wh/L, about 0.1 Wh/L to about 0.4 Wh/L, about 0.1 Wh/Lto about 0.5 Wh/L, about 0.2 Wh/L to about 0.3 Wh/L, about 0.2 Wh/L toabout 0.4 Wh/L, about 0.2 Wh/L to about 0.5 Wh/L, about 0.3 Wh/L toabout 0.4 Wh/L, about 0.3 Wh/L to about 0.5 Wh/L or about 0.4 Wh/L toabout 0.5 Wh/L.

In some embodiments the superconductor has a volumetric power density ofat least about 7 kW/L. In some embodiments, the superconductor has avolumetric power density of at most about 30 kW/L. In some embodiments,the superconductor has a volumetric power density of about 7 kW/L toabout 30 kW/L. In some embodiments the superconductor has a volumetricpower density of about 7 kW/L to about 10 kW/L, about 7 kW/L to about 15kW/L, about 7 kW/L to about 20 kW/L, about 7 kW/L to about 25 kW/L,about 7 kW/L to about 30 kW/L, about 10 kW/L to about 15 kW/L, about 10kW/L to about 20 kW/L, about 10 kW/L to about 25 kW/L, about 10 kW/L toabout 30 kW/L, about 15 kW/L to about 20 kW/L, about 15 kW/L to about 25kW/L, about 15 kW/L to about 30 kW/L, about 20 kW/L to about 25 kW/L,about 20 kW/L to about 30 kW/L or about 25 kW/L to about 30 kW/L.

Another aspect provided herein is a method of fabricating a grapheneoxide film, comprising: dispersing graphene oxide; filtering thegraphene oxide through a membrane to form a graphene oxide film on themembrane; freeze-casting the graphene oxide film on the membrane; andpeeling the graphene oxide film off the membrane.

In some embodiments, the graphene oxide film exhibits a thickness ofabout 6 μm to about 16 μm, about 16 μm to about 32 μm, or about 32 μm toabout 60 μm.

In some embodiments, the graphene oxide is synthesized by a modifiedHummer's method.

In some embodiments, the graphene oxide is prepared from naturalgraphite flakes.

In some embodiments, the process of dispersing graphene oxide comprises:suspending the graphene oxide in a fluid; and forming a solution of thesuspended graphene oxide and an acid, wherein the fluid comprises water,formic acid, n-butanol, isopropanol, n-propanol, ethanol, methanol,acetic acid or any combination thereof.

In some embodiments the concentration of graphene oxide in the fluid isat least about 1 mg/ml. In some embodiments, the concentration ofgraphene oxide in the fluid is at most about 6 mg/ml. In someembodiments, the concentration of graphene oxide in the fluid is about 1mg/ml to about 6 mg/ml. In some embodiments the concentration ofgraphene oxide in the fluid is about 1 mg/ml to about 2 mg/ml, about 1mg/ml to about 3 mg/ml, about 1 mg/ml to about 4 mg/ml, about 1 mg/ml toabout 5 mg/ml, about 1 mg/ml to about 6 mg/ml, about 2 mg/ml to about 3mg/ml, about 2 mg/ml to about 4 mg/ml, about 2 mg/ml to about 5 mg/ml,about 2 mg/ml to about 6 mg/ml, about 3 mg/ml to about 4 mg/ml, about 3mg/ml to about 5 mg/ml, about 3 mg/ml to about 6 mg/ml, about 4 mg/ml toabout 5 mg/ml, about 4 mg/ml to about 6 mg/ml or about 5 mg/ml to about6 mg/ml. In some embodiments, the graphene oxide film has a thickness ofabout 16 m to about 32 μm.

In some embodiments the volume of suspended graphene oxide in thesolution is at least about 0.5 ml. In some embodiments, the volume ofsuspended graphene oxide in the solution is at most about 2 ml. In someembodiments, the volume of suspended graphene oxide in the solution isabout 0.5 ml to about 2 ml. In some embodiments the volume of suspendedgraphene oxide in the solution is about 0.5 ml to about 1 ml, about 0.5ml to about 1.5 ml, about 0.5 ml to about 2 ml, about 1 ml to about 1.5ml, about 1 ml to about 2 ml or about 1.5 ml to about 2 ml.

In some embodiments the mass of the acid in the solution is at leastabout 3 mg. In some embodiments, the mass of the acid in the solution isat most about 15 mg. In some embodiments, the mass of the acid in thesolution is about 3 mg to about 15 mg. In some embodiments the mass ofthe acid in the solution is about 3 mg to about 6 mg, about 3 mg toabout 9 mg, about 3 mg to about 12 mg, about 3 mg to about 15 mg, about6 mg to about 9 mg, about 6 mg to about 12 mg, about 6 mg to about 15mg, about 9 mg to about 12 mg, about 9 mg to about 15 mg or about 12 mgto about 15 mg.

In some embodiments, the graphene oxide film has a thickness of about 16μm to about 32 μm.

In some embodiments the volume of suspended graphene oxide in thesolution is at least about 1 ml. In some embodiments, the volume ofsuspended graphene oxide in the solution is at most about 4 ml. In someembodiments, the volume of suspended graphene oxide in the solution isabout 1 ml to about 4 ml. In some embodiments the volume of suspendedgraphene oxide in the solution is about 1 ml to about 2 ml, about 1 mlto about 3 ml, about 1 ml to about 4 ml, about 2 ml to about 3 ml, about2 ml to about 4 ml or about 3 ml to about 4 ml.

In some embodiments the mass of the acid in the solution is at leastabout 7 mg. In some embodiments, the mass of the acid in the solution isat most about 30 mg. In some embodiments, the mass of the acid in thesolution is about 7 mg to about 30 mg. In some embodiments the mass ofthe acid in the solution is about 7 mg to about 10 mg, about 7 mg toabout 15 mg, about 7 mg to about 20 mg, about 7 mg to about 25 mg, about7 mg to about 30 mg, about 10 mg to about 15 mg, about 10 mg to about 20mg, about 10 mg to about 25 mg, about 10 mg to about 30 mg, about 15 mgto about 20 mg, about 15 mg to about 25 mg, about 15 mg to about 30 mg,about 20 mg to about 25 mg, about 20 mg to about 30 mg or about 25 mg toabout 30 mg.

In some embodiments, the graphene oxide film has a thickness of about 32μm to about 60 μm.

In some embodiments the volume of suspended graphene oxide in thesolution is at least about 2 ml. In some embodiments, the volume ofsuspended graphene oxide in the solution is at most about 10 ml. In someembodiments, the volume of suspended graphene oxide in the solution isabout 2 ml to about 10 ml. In some embodiments the volume of suspendedgraphene oxide in the solution is about 2 ml to about 4 ml, about 2 mlto about 6 ml, about 2 ml to about 8 ml, about 2 ml to about 10 ml,about 4 ml to about 6 ml, about 4 ml to about 8 ml, about 4 ml to about10 ml, about 6 ml to about 8 ml, about 6 ml to about 10 ml or about 8 mlto about 10 ml.

In some embodiments the mass of the acid in the solution is at leastabout 15 mg. In some embodiments, the mass of the acid in the solutionis at most about 70 mg. In some embodiments, the mass of the acid in thesolution is about 15 mg to about 70 mg. In some embodiments the mass ofthe acid in the solution is about 15 mg to about 30 mg, about 15 mg toabout 45 mg, about 15 mg to about 60 mg, about 15 mg to about 70 mg,about 30 mg to about 45 mg, about 30 mg to about 60 mg, about 30 mg toabout 70 mg, about 45 mg to about 60 mg, about 45 mg to about 70 mg orabout 60 mg to about 70 mg.

In some embodiments, the acid comprises a weak acid, wherein the weakacid comprises formic acid, citric acid, acetic acid, ascorbic acid,malic acid, tartaric acid, propionic acid, butyric acid, valeric acid,caprioc acid, oxalic acid, benzoic acid, carbonic acid or anycombination thereof.

In some embodiments, the method of fabricating a supercapacitor furthercomprises shaking the solution, wherein the shaking of the solution isvigorous.

In some embodiments the shaking of the solution occurs over a period ofat least about 1 minute. In some embodiments, the shaking of thesolution occurs over a period of at most about 10 minutes. In someembodiments, the shaking of the solution occurs over a period of about 1minute to about 10 minutes. In some embodiments the shaking of thesolution occurs over a period of about 1 minute to about 2 minutes,about 1 minute to about 4 minutes, about 1 minute to about 6 minutes,about 1 minute to about 8 minutes, about 1 minute to about 10 minutes,about 2 minutes to about 4 minutes, about 2 minutes to about 6 minutes,about 2 minutes to about 8 minutes, about 2 minutes to about 10 minutes,about 4 minutes to about 6 minutes, about 4 minutes to about 8 minutes,about 4 minutes to about 10 minutes, about 6 minutes to about 8 minutes,about 6 minutes to about 10 minutes or about 8 minutes to about 10minutes.

In some embodiments, the method of fabricating a supercapacitor furthercomprises a step of partially reducing the graphene oxide, wherein thestep of partially reducing the graphene oxide occurs before the step ofstep of filtering the graphene oxide, wherein the step of partiallyreducing the graphene oxide comprises heating the dispersed grapheneoxide.

In some embodiments the heating of the solution occurs at a temperatureof at least about 25° C. In some embodiments, the heating of thesolution occurs at a temperature of at most about 100° C. In someembodiments, the heating of the solution occurs at a temperature ofabout 25° C. to about 100° C. In some embodiments the heating of thesolution occurs at a temperature of about 25° C. to about 50° C., about25° C. to about 75° C., about 25° C. to about 100° C., about 50° C. toabout 75° C., about 50° C. to about 100° C. or about 75° C. to about100° C.

In some embodiments the heating of the solution occurs over a period ofat least about 1 minute. In some embodiments, the heating of thesolution occurs over a period of at most about 100 minutes. In someembodiments, the heating of the solution occurs over a period of about 1minute to about 100 minutes. In some embodiments the heating of thesolution occurs over a period of about 1 minute to about 10 minutes,about 1 minute to about 20 minutes, about 1 minute to about 50 minutes,about 1 minute to about 75 minutes, about 1 minute to about 100 minutes,about 10 minutes to about 20 minutes, about 10 minutes to about 50minutes, about 10 minutes to about 75 minutes, about 10 minutes to about100 minutes, about 20 minutes to about 50 minutes, about 20 minutes toabout 75 minutes, about 20 minutes to about 100 minutes, about 50minutes to about 75 minutes, about 50 minutes to about 100 minutes orabout 75 minutes to about 100 minutes.

In some embodiments, the membrane comprises cellulose, cellulose ester,cellulose acetate, polysulfone, polyethersulfone, etched polycarbonate,collagen or any combination thereof. In some embodiments the membranehas a pore size of at least about 0.1 μm. In some embodiments, themembrane has a pore size of at most about 0.5 _(μ)m. In someembodiments, the membrane has a pore size of about 0.1 _(μ)m to about0.5 _(μ)m. In some embodiments the membrane has a pore size of about 0.1μm to about 0.2 μm, about 0.1 μm to about 0.3 μm, about 0.1 μm to about0.4 μm, about 0.1 μm to about 0.5 μm, about 0.2 μm to about 0.3 μm,about 0.2 μm to about 0.4 μm, about 0.2 _(μ)m to about 0.5 _(μ)m, about0.3 _(μ)m to about 0.4 _(μ)m, about 0.3 _(μ)m to about 0.5 _(μ)m orabout 0.4 μm to about 0.5 μm.

Some embodiments, further comprise terminating the filtration once themembrane contains no visible dispersed graphene oxide.

In some embodiments, the step of freeze-casting the graphene oxide filmon the membrane comprises: freezing the graphene oxide film on themembrane, and immersing the graphene oxide film on the membrane in afluid.

In some embodiments, the freezing of the graphene oxide film on themembrane is performed by liquid nitrogen, dry ice, ethanol or anycombination thereof.

In some embodiments the freezing occurs over a period of time of atleast about 15 minutes. In some embodiments, the freezing occurs over aperiod of time of at most about 60 minutes. In some embodiments, thefreezing occurs over a period of time of about 15 minutes to about 60minutes. In some embodiments the freezing occurs over a period of timeof about 15 minutes to about 20 minutes, about 15 minutes to about 25minutes, about 15 minutes to about 30 minutes, about 15 minutes to about35 minutes, about 15 minutes to about 40 minutes, about 15 minutes toabout 45 minutes, about 15 minutes to about 50 minutes, about 15 minutesto about 55 minutes, about 15 minutes to about 60 minutes, about 20minutes to about 25 minutes, about 20 minutes to about 30 minutes, about20 minutes to about 35 minutes, about 20 minutes to about 40 minutes,about 20 minutes to about 45 minutes, about 20 minutes to about 50minutes, about 20 minutes to about 55 minutes, about 20 minutes to about60 minutes, about 25 minutes to about 30 minutes, about 25 minutes toabout 35 minutes, about 25 minutes to about 40 minutes, about 25 minutesto about 45 minutes, about 25 minutes to about 50 minutes, about 25minutes to about 55 minutes, about 25 minutes to about 60 minutes, about30 minutes to about 35 minutes, about 30 minutes to about 40 minutes,about 30 minutes to about 45 minutes, about 30 minutes to about 50minutes, about 30 minutes to about 55 minutes, about 30 minutes to about60 minutes, about 35 minutes to about 40 minutes, about 35 minutes toabout 45 minutes, about 35 minutes to about 50 minutes, about 35 minutesto about 55 minutes, about 35 minutes to about 60 minutes, about 40minutes to about 45 minutes, about 40 minutes to about 50 minutes, about40 minutes to about 55 minutes, about 40 minutes to about 60 minutes,about 45 minutes to about 50 minutes, about 45 minutes to about 55minutes, about 45 minutes to about 60 minutes, about 50 minutes to about55 minutes, about 50 minutes to about 60 minutes or about 55 minutes toabout 60 minutes.

In some embodiments, freezing of the graphene oxide film on the membraneis performed by vertical immersion.

In some embodiments, freezing of the graphene oxide film on the membraneis performed by horizontal immersion.

Some embodiments further comprise thawing the graphene oxide film on themembrane.

In some embodiments, thawing of the graphene oxide film on the membraneoccurs at room temperature.

In some embodiments, thawing of the graphene oxide film on the membraneis performed after the freezing of the graphene oxide film on themembrane.

Some embodiments further comprise transferring the graphene oxide filmon the membrane into a container.

In some embodiments, transferring of the graphene oxide film on themembrane into a container is performed after the thawing of the grapheneoxide film on the membrane.

In some embodiments, the container comprises a vial, a cup, a jar, abowl, a dish, a flask, a beaker or any combination thereof.

In some embodiments, the container is comprised of glass, plastic,metal, wood, carbon fiber, fiberglass or any combination thereof.

Some embodiments further comprise heating the graphene oxide film on themembrane.

In some embodiments, the heating of the graphene oxide film on themembrane is performed after the thawing of the graphene oxide film onthe membrane.

In some embodiments, the heating of the graphene oxide film on themembrane is performed after the transferring of the graphene oxide filmon the membrane into a container.

In some embodiments the heating the graphene oxide film on the membraneoccurs at a temperature of at least about 50° C. In some embodiments,the heating the graphene oxide film on the membrane occurs at atemperature of at most about 200° C. In some embodiments, the heatingthe graphene oxide film on the membrane occurs at a temperature of about50° C. to about 200° C. In some embodiments the heating the grapheneoxide film on the membrane occurs at a temperature of about 50° C. toabout 75° C., about 50° C. to about 100° C., about 50° C. to about 125°C., about 50° C. to about 150° C., about 50° C. to about 175° C., about50° C. to about 200° C., about 75° C. to about 100° C., about 75° C. toabout 125° C., about 75° C. to about 150° C., about 75° C. to about 175°C., about 75° C. to about 200° C., about 100° C. to about 125° C., about100° C. to about 150° C., about 100° C. to about 175° C., about 100° C.to about 200° C., about 125° C. to about 150° C., about 125° C. to about175° C., about 125° C. to about 200° C., about 150° C. to about 175° C.,about 150° C. to about 200° C. or about 175° C. to about 200° C.

In some embodiments the heating the graphene oxide film on the membraneoccurs over a period of time of at least about 5 hours. In someembodiments, the heating the graphene oxide film on the membrane occursover a period of time of at most about 30 hours. In some embodiments,the heating the graphene oxide film on the membrane occurs over a periodof time of about 5 hours to about 30 hours. In some embodiments theheating the graphene oxide film on the membrane occurs over a period oftime of about 5 hours to about 10 hours, about 5 hours to about 15hours, about 5 hours to about 20 hours, about 5 hours to about 25 hours,about 5 hours to about 30 hours, about 10 hours to about 15 hours, about10 hours to about 20 hours, about 10 hours to about 25 hours, about 10hours to about 30 hours, about 15 hours to about 20 hours, about 15hours to about 25 hours, about 15 hours to about 30 hours, about 20hours to about 25 hours, about 20 hours to about 30 hours or about 25hours to about 30 hours.

In some embodiments, the fluid comprises a solvent, wherein the solventcomprises tetrahydrofuran, ethyl acetate, dimethylformamide,acetonitrile, acetone, dimethyl sulfoxide, nitromethane, propylenecarbonate, ethanol, formic acid, n-butanol, methanol, acetic acid,water, deionized water or any combination thereof.

In some embodiments the immersing of the membrane and the partiallyreduced graphene occurs over a period of time of at least about 5 hours.In some embodiments, the immersing of the membrane and the partiallyreduced graphene occurs over a period of time of at most about 30 hours.

In some embodiments, the immersing of the membrane and the partiallyreduced graphene occurs over a period of time of about 5 hours to about30 hours. In some embodiments the immersing of the membrane and thepartially reduced graphene occurs over a period of time of about 5 hoursto about 10 hours, about 5 hours to about 15 hours, about 5 hours toabout 20 hours, about 5 hours to about 25 hours, about 5 hours to about30 hours, about 10 hours to about 15 hours, about 10 hours to about 20hours, about 10 hours to about 25 hours, about 10 hours to about 30hours, about 15 hours to about 20 hours, about 15 hours to about 25hours, about 15 hours to about 30 hours, about 20 hours to about 25hours, about 20 hours to about 30 hours or about 25 hours to about 30hours.

Some embodiments further comprise cutting the graphene oxide film on themembrane into pieces.

In some embodiments the pieces of graphene oxide film have a surfacearea of at least about 0.5 cm². In some embodiments, the pieces ofgraphene oxide film have a surface area of at most about 2 cm². In someembodiments, the pieces of graphene oxide film have a surface area ofabout 0.5 cm² to about 2 cm². In some embodiments the pieces of grapheneoxide film have a surface area of about 0.5 cm² to about 1 cm², about0.5 cm² to about 1.5 cm², about 0.5 cm² to about 2 cm², about 1 cm² toabout 1.5 cm², about 1 cm² to about 2 cm² or about 1.5 cm² to about 2cm².

Some embodiments further comprise immersing the graphene oxide films inan electrolyte.

In some embodiments, the electrolyte is aqueous, wherein the electrolytecomprises an acid, wherein the acid is a strong acid, wherein the strongacid comprises perchloric acid, hydroiodic acid, hydrobromic acid,hydrochloric acid, sulfuric acid, p-toluenesulfonic acid methanesulfonicacid, or any combination thereof.

In some embodiments the electrolyte has a concentration of at leastabout 0.5 M. In some embodiments, the electrolyte has a concentration ofat most about 2 M. In some embodiments, the electrolyte has aconcentration of about 0.5 M to about 2 M. In some embodiments theelectrolyte has a concentration of about 0.5 M to about 1 M, about 0.5 Mto about 1.5 M, about 0.5 M to about 2 M, about 1 M to about 1.5 M,about 1 M to about 2 M or about 1.5 M to about 2 M.

In some embodiments the immersing of the graphene oxide film occurs overa period of time of at least about 5 hours. In some embodiments, theimmersing of the graphene oxide film occurs over a period of time of atmost about 30 hours. In some embodiments, the immersing of the grapheneoxide film occurs over a period of time of about 5 hours to about 30hours. In some embodiments the immersing of the graphene oxide filmoccurs over a period of time of about 5 hours to about 10 hours, about 5hours to about 15 hours, about 5 hours to about 20 hours, about 5 hoursto about 25 hours, about 5 hours to about 30 hours, about 10 hours toabout 15 hours, about 10 hours to about 20 hours, about 10 hours toabout 25 hours, about 10 hours to about 30 hours, about 15 hours toabout 20 hours, about 15 hours to about 25 hours, about 15 hours toabout 30 hours, about 20 hours to about 25 hours, about 20 hours toabout 30 hours or about 25 hours to about 30 hours.

Some embodiments further comprise placing the graphene oxide films on ametallic foil, wherein the metallic foil comprises Scandium, Titanium,Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc,Yttrium, Zirconium, Niobium, Molybdenum, Technetium, Ruthenium, Rhodium,Palladium, Silver, Cadmium, Hafnium, Tantalum, Tungsten, Rhenium,Osmium, Iridium, Platinum, Gold, Mercury or any combination thereof.

Other goals and advantages of the invention will be further appreciatedand understood when considered in conjunction with the followingdescription and accompanying drawings. While the following descriptionmay contain specific details describing particular embodiments of theinvention, this should not be construed as limitations to the scope ofthe invention but rather as an exemplification of preferableembodiments. For each aspect of the invention, many variations arepossible as suggested herein that are known to those of ordinary skillin the art. A variety of changes and modifications may be made withinthe scope of the invention without departing from the spirit thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings or figures (also “FIG.” and “FIGS.” herein), ofwhich:

FIG. 1 shows an exemplary schematic illustration of the formation of aporous graphene film through pre-reduction, filtration andfreeze-casting, an exemplary water phase diagram, and an exemplarycross-section Scanning Electron Microscope (SEM) image of a porousgraphene film.

FIGS. 2A-B show an exemplary schematic illustration of ion and electrontransport in a three dimensional (3D) porous reduced graphene oxide(RGO) film and an RGO film.

FIG. 3 shows an exemplary Randles equivalent circuit of asuperconductor.

FIGS. 4A-B show an exemplary schematic illustration of the interfacialfree energies between the solvent solidification front and the particlesin suspension.

FIG. 5 shows a schematic illustration of an exemplary structure of asymmetric two-electrode supercapacitor.

FIGS. 6A-D show scanning electron microscope (SEM) images of exemplarypartially reduced GO samples with different reduction times.

FIGS. 7A-D show cross-section SEM images of exemplary 3D porous RGOfilms with different pre-reduction times.

FIGS. 8A-B show cross-section SEM images of exemplary RGO films underlow and high magnifications.

FIGS. 9A-B show cross-section SEM images of exemplary 3D porous RGOfilms with different loading masses.

FIGS. 10A-H show SEM images of exemplary 3D porous RGO films afterlong-term reduction, a photograph of an exemplary bent 3D porous RGOfilm, and transmission electron microscope (TEM) images of exemplarygraphene films and pores.

FIG. 11 shows an exemplary atomic-force microscopy (AFM) image of GOsheets.

FIGS. 12A-B show an exemplary height distribution diagram and anexemplary line scan profile.

FIG. 13 shows x-ray power diffraction (XRD) patterns for the exemplarysamples of GO, pre-reduced GO, and 3D porous RGO film under differentreduction procedures.

FIGS. 14A-C show exemplary x-ray photoelectric spectroscopy (XPS) C_(1s)transition profiles for GO, pre-reduced GO and 3D porous RGO films.

FIG. 15 shows Raman spectra for exemplary GO, pre-reduced GO and 3Dporous RGO films.

FIG. 16 shows an exemplary schematic illustration of a two-electrodemeasurement system. FIGS. 17A-D show the I-V curves, and a comparison ofelectrical conductivity values of exemplary 3D porous RGO, partialreduced GO, and GO films

FIG. 18 shows the strain-stress curve of an exemplary 3D porous RGOfilm.

FIGS. 19A-D show cyclic voltammetry profiles and the dependence of thedischarge current on voltage scan rates, of an exemplary RGO filmsupercapacitor in 1.0 M H₂SO₄ aqueous electrolyte.

FIGS. 20A-D show cyclic voltammetry profiles and the dependence of thedischarge current on voltage scan rates for an exemplary 3D porous RGOfilm supercapacitor in 1.0 M H₂SO₄ aqueous electrolyte.

FIGS. 21A-F show cyclic voltammetry profiles at different scan rates foran exemplary 3D porous RGO film in 1.0 M H₂SO₄ electrolyte andperformance comparisons of an exemplary 3D porous RGO film and anexemplary RGO film based supercapacitor.

FIGS. 22A-D show comparative cyclic voltammetry curves of exemplary 3Dporous RGO, the gravimetric and areal capacitance of exemplary 3D porousRGO electrodes with different mass loadings at various currentdensities, and a Ragone plot of the volumetric power density versusenergy density for exemplary 3D porous RGO supercapacitors.

FIG. 23 shows galvanostatic charge/discharge profiles for exemplary RGOand 3D porous RGO films at a current density of 100 A/g.

FIG. 24 shows exemplary illustrations of GO dispersions after beingsubjected to pre-reduction by ascorbic acid for different times.

DETAILED DESCRIPTION

Provided herein are graphene materials, fabrication processes anddevices with improved performance. In some embodiments, the presentdisclosure provides supercapacitors comprising a graphene material andtheir fabrication processes. Such supercapacitors may avoid theshortcomings of current energy storage technologies. A supercapacitor ofthe present disclosure may comprise one or more supercapacitor cells. Asupercapacitor may comprise a positive electrode and a negativeelectrode separated by a separator comprising an electrolyte. Thepositive electrode may be a cathode during discharge. The negativeelectrode may be an anode during discharge. In some embodiments, aplurality of supercapacitor cells may be arranged (e.g., interconnected)in a pack.

Provided herein are supercapacitor devices and methods for fabricationthereof. The supercapacitor devices may be electrochemical devices. Thesupercapacitor devices may be configured for high energy and/or powerdensity. The supercapacitor devices of the disclosure may include anelectrode composed of three-dimensional (3D) hierarchical porousfilm(s). The supercapacitor devices of the disclosure may compriseinterconnected devices.

Provided herein are methods, devices and systems for the preparation andprocessing of graphene into three-dimensional hierarchical porouselectrode films. Some embodiments provide systems and methods forfabricating electrode films with a controlled porosity and a highsurface area. Some embodiments provide systems and methods forfabricating 3D hierarchical porous films through filtering andfreeze-casting partially reduced graphene oxide. The processes describedherein may include the manufacture (or synthesis) of graphene oxide; themanufacture (or synthesis) of reduced graphene oxide; and/or themanufacture (or synthesis) of three-dimensional reduced graphene oxide.

Various aspects of the disclosure described herein may be applied to anyof the particular applications set forth below or in any other type ofmanufacturing, synthesis or processing setting. Other manufacturing,synthesis or processing of materials may equally benefit from featuresdescribed herein. For example, the methods, devices and systems hereinmay be advantageously applied to manufacture (or synthesis) of variousforms of graphene oxide. The invention may be applied as a standalonemethod, device or system, or as part of an integrated manufacturing ormaterials (e.g., chemicals) processing system. It shall be understoodthat different aspects of the invention may be appreciated individually,collectively, or in combination with each other.

An aspect of the invention provides supercapacitor devices comprisingone or more electrodes, each composed of three-dimensional hierarchicalporous film(s), and electrolytes disposed between the electrodes.

Reference will now be made to the figures. It will be appreciated thatthe figures and features therein are not necessarily drawn to scale. Theschematic illustrations, images, formulas, charts and graphs referred toherein represent fabricated exemplary devices that serve as arepresentation of the appearance, characteristics and functionality ofthe devices produced by the exemplary methods described herein.

Device Capabilities

An energy storage device (e.g., supercapacitor) of the presentdisclosure may have a power density at least about 1.5, 2, 5, 10, 20,50, 100, 200 or 300 times greater than a supercapacitor available in themarket (e.g., a supercapacitor with a power density of 1-10 kW/kg). Anenergy storage device (e.g., supercapacitor) of the present disclosuremay have cycling stability or cycle life at least about 1.5, 2 or 2.5times greater than a supercapacitor available in the market (e.g., asupercapacitor with a cycling stability or cycle life of 500 cycles).For example, an energy storage device (e.g., supercapacitor) of thepresent disclosure may run electronic device(s) for twice as long andmay be used for more than 5000 cycles compared to only 500 cycles forcompetitive technologies.

The supercapacitors described herein may play an important role in oneor more applications or areas, such as, for example, portableelectronics (e.g., cellphones, computers, cameras, etc.), medicaldevices (e.g., life-sustaining and life-enhancing medical devices,including pacemakers, defibrillators, hearing aids, pain managementdevices, and drug pumps, electric vehicles (e.g., energy storage deviceswith long lifetime are needed to improve the electric vehicles industry,space (e.g., the energy storage devices may be used in space to powerspace systems including rovers, landers, spacesuits and electronicequipment), military energy storage devices (e.g., the military usesspecial energy storage devices for powering a large number ofelectronics and equipment; reduced mass/volume of the energy storagedevices described herein are highly preferred), electric aircraft (e.g.,an aircraft that runs on electric motors rather than internal combustionengines, with electricity coming from solar cells or energy storagedevices), grid scale energy storage (e.g., energy storage devices may beused to store electrical energy during times when production (from powerplants) exceeds consumption and the stored energy may be used at timeswhen consumption exceeds production), renewable energy (e.g., since thesun does not shine at night and the wind does not blow at all times,energy storage devices in off-the-grid power systems may store excesselectricity from renewable energy sources for use during hours aftersunset and when the wind is not blowing; high power energy storagedevices may harvest energy from solar cells with higher efficiency thancurrent state-of-the-art energy storage devices), power tools (e.g., theenergy storage devices described herein may enable fast-chargingcordless power tools such as drills, screwdrivers, saws, wrenches andgrinders; current energy storage devices have a long recharging time),or any combination thereof.

Energy Storage Devices

Energy storage devices of the present disclosure may comprise at leastone electrode (e.g., a positive electrode and a negative electrode). Thegraphene material of the present disclosure may be provided in thepositive electrode (cathode during discharge), the negative electrode(anode during discharge) or both. In certain embodiments, the energystorage device may be a supercapacitor.

In some embodiments, supercapacitors, otherwise called electrochemicalcapacitors, are solid-state energy storage devices with a much highercapacitance, and which may recharged a hundred to a thousand timesfaster, than normal capacitors. Some supercapacitors may contain powerdensities in excess of 10 kW/kg; 10 times larger than currentlithium-ion batteries. Unlike batteries, whose charging and dischargingspeed may be limited by chemical reactions, supercapacitors store chargethrough highly reversible ion absorption and/or redox reactions, whichenable fast energy capture and delivery.

In some embodiments, supercapacitors may exhibit a high power densityand excellent low-temperature performance, and as such, have beenincreasingly employed as energy storage resources in such applicationsas portable electronic devices, medical devices, back-up power devices,flash cameras, factories, regenerative braking systems and hybridelectric vehicles. Although some current supercapacitors have shownsignificant gains in energy density, these devices may exhibit a loss ofpower and/or cycling capability over time. High power density maycontinue to attract increasing attention, especially for conditions inwhich huge amounts of energy need to be input or output in a limitedtime, such as load-leveling the emerging smart electrical grid, flashcharging electronics and quick acceleration for electric vehicles.

In some embodiments, supercapacitors are flexible and able to bend andflex over a certain range of motion without breaking or degrading. Suchflexible electronics, also known as flex circuits, may be composed ofelectronic circuits mounted to, or printed on, flexible substrates toproduce portable and rugged products.

In some embodiments, supercapacitors are comprised of two or moreelectrodes, each separated by an ion-permeable membrane (separator), andan electrolyte ionically connecting the electrodes, whereas ions in theelectrolyte form electric double layers of opposite polarity to theelectrodes' polarities when the electrodes are polarized by an appliedvoltage.

Supercapacitors may be divided into two main categories depending on themechanism of charge storage: redox supercapacitors, and electricdouble-layer capacitors. Additionally, a supercapacitor may be symmetricor asymmetric with electrodes that are identical or dissimilar,respectively.

In some embodiments, a supercapacitor electrode may comprise an activematerial and/or a substrate. The active material of a supercapacitorelectrode may comprise a transition-metal oxide, a conducting polymer, ahigh-surface carbon or any combination thereof. As active materials aretypically porous and thus brittle and poor conductors, a substrate, orcurrent collector, may be employed as a support structure and aconducting path to decrease the resistance of the supercapacitor.Current collectors may be comprised of carbon cloth silicon, metaloxide, gallium arsenide, glass, steel, stainless steel or anycombination thereof. Some supercapacitor electrode collectors may bedesigned to flex and bend under stress. An electrode of anelectrochemical cell in which electrons leave the active material withincell and oxidation occurs may be referred to as an anode. An electrodeof an electrochemical cell in which the electrons enter the activematerial within cell and reduction occurs may be referred to as acathode. Each electrode may become either an anode or a cathodedepending on the direction of current through the cell.

In some embodiments, the electrode material may strongly affect theenergy storage performance of a supercapacitor. Electrode materials withhigh surface areas allow for increased charge quantity and speed ofcharge storage. Some currently available supercapacitors exhibit alimited power density because their activated carbon electrodes containa limited microporous structure. There is a current unmet need for anelectrode with a controllable pore size, electronic conductivity, andloading mass for supercapacitor devices with high energy density.

In some embodiments, electrodes are composed of graphene, a oneatom-thin two-dimensional flake of carbon that may exhibit a highelectrical conductivity, a high surface area-to-weight ratio, and a widestable potential window. Graphene film, an important macroscopicstructure of graphene alternatively called graphene paper, may beproduced by a number of methods comprising blade-coating, spray-coating,layer-by-layer assembly, interfacial self-assembly, filtration assemblyor any combination thereof. The shear stress, interfacial tension orvacuum compression methods inherent in the current graphene filmmanufacturing methods, however, may often restack the two-dimensionallayered graphene sheets to form dense layered graphene films, whoselamellar microstructures exhibit less surface area than graphene flakes.The dense layered graphene films produced by the current methods maylack a sufficiently open continuous hierarchical of pores that serve asion-buffering reservoirs and high speed ion transport channels foreffective electrochemical kinetic processes. As such, supercapacitordevices employing dense layered graphene films may exhibit poorelectro-capacitive performance capabilities including low powerdensities and long charging times. In some embodiments, application of3D hierarchical porous films within supercapacitors may result insupercapacitors with high power densities. The schematic illustrationspresented in FIGS. 2A-B shows the easier ion diffusion and minimizedelectron transport resistance for an exemplary 3D porous RGO filmcompared with an exemplary RGO film. The unique properties of 3D porousRGO films may enable their excellent performance as supercapacitorelectrodes.

In some embodiments, a supercapacitor device contains an electrolyte.Electrolytes may include, for example, aqueous, organic and/or ionicliquid-based electrolytes. The electrolyte may be liquid, solid or agel. In some embodiments, the performance of supercapacitors withgraphene electrodes may be improved by employing a nonvolatile liquidelectrolyte that may serve as an effective “spacer” to prevent theirreversible n-n stacking between graphene sheets.

In some embodiments, the energy storage device may comprise a separator.For example, the energy storage device may comprise a polyethyleneseparator (e.g., an ultra-high molecular weight polyethylene separator).The separator may have a thickness of less than or equal to about 16 μm,15 μm, 14 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm or 8 μm (e.g., about12±2.0 μm). The separator may have a given permeability. The separatormay have a permeability (e.g., Gurley type) of greater than or equal toabout 150 sec/100 ml, 160 sec/100 ml. 170 sec/100 ml, 180 sec/100 ml,190 sec/100 ml, 200 sec/100 ml, 210 sec/100 ml, 220 sec/100 ml, 230sec/100 ml, 240 sec/100 ml, 250 sec/100 ml, 260 sec/100 ml, 270 sec/100ml, 280 sec/100 ml, 290 sec/100 ml or 300 sec/100 ml (e.g., 180±50sec/100 ml). Alternatively, the separator may have a permeability (e.g.,Gurley type) of less than about 150 sec/100 ml, 160 sec/100 ml. 170sec/100 ml, 180 sec/100 ml, 190 sec/100 ml, 200 sec/100 ml, 210 sec/100ml, 220 sec/100 ml, 230 sec/100 ml, 240 sec/100 ml, 250 sec/100 ml, 260sec/100 ml, 270 sec/100 ml, 280 sec/100 ml, 290 sec/100 ml or 300sec/100 ml. The separator may have a given porosity. The separator mayhave a porosity of greater than or equal to about 35%, 40%,45% or 50%(e.g., 40±5%). Alternatively, the separator may have a porosity of lessthan about 35%, 40%, 45% or 50%. The separator may have a givenshut-down temperature (e.g., above the shut-down temperature, theseparator may not function normally). In some embodiments, the separatormay have a shut-down temperature (actual) of less than or equal to about150° C., 140° C., 130° C., 120° C., 110° C. or 100° C. In someembodiments, the separator may have a shut-down temperature (DSC)between about 130° C. and 150° C., 130° C. and 140° C., or 136° C. and140° C.

FIG. 5, schematically illustrates the architecture of an exemplarysupercapacitor, comprising a first current collector 501, a firstelectrode 502, an electrolyte 503, a separator 504, a second electrode505 and a second current collector 506. Per the exemplary illustrationin FIG. 5, a first electrode 502 serves as a cathode and the secondelectrode 505 serves as an anode.

Methods of Formulating Supercapacitor Electrodes

FIG. 1 schematically illustrates the formation of a porous graphene film105 comprising the steps of graphite oxide (GO) dispersion 101, partialpre-reduction of the GO 102, reduced GO filtering 103, andfreeze-casting. The water phase diagram shows the status of the aqueoussolution during the different procedures and a typical cross-section SEMimage of an exemplary porous graphene film.

In some embodiments, graphene oxide (GO), may be produced in bulk fromgraphite at low cost, as a precursor to fabricate porous graphene films.FIG. 11 shows an exemplary atomic-force microscopy (AFM) image of GOsheets, FIGS. 12A-B show an exemplary height distribution diagram andthe profile of the line scan from the exemplary AFM image in FIG. 11,whereas GO sheets may be several micrometers thick, and are typicallyapproximately 1.2 nm thick. 1.2 nm thick.

In some embodiments, a GO monolayer exhibits a thickness ofapproximately 1-1.4 nm thick, larger than an ideal monolayer of graphene(thickness 0.34 nm), due to the presence of functional groups andadsorbed molecules. Since the functional groups may make GO stronglyhydrophilic and negatively charged, the single layer GO sheets may behomogeneously dispersed 101 in an aqueous solution.

The requisite for a pre-reduction step 102 before freeze casting to forma hierarchy of pores within a graphene film may stem from two propertiesof GO. First, the 3D micro-gel structures may effectively resist theaggregation of the GO sheets during the filtration assembly and leavesufficient space for the solidification of water. In contrast, thecompact configuration of filtered 2D GO sheets may jam theredistribution during the freezing procedure. Second, during the growthof GO sheets into micro-gels, the particle size may increase, and the 2Dlamellar sheets may become 3D micro networks. In order to assemble intoan integral porous graphene film, the GO particles in suspension may berejected from the advancing solidification front during freezing. Thethermodynamic condition for a GO particle to be rejected by thesolidification front is that the interfacial free energies satisfyingthis following criterion:

Δσ=Δσ_(SP)−(Δσ_(LP)+Δσ_(SL))>0

where σ_(SP), σ_(LP), and σ_(SL) are the interfacial free energiesassociated with the solid (ice)-particle (pre-reduced GO micro-gel or GOsheets), liquid (water)-particle and solid-liquid interfacerespectively. As illustrated in FIGS. 4A-B, the size increase andmorphology change may reduce the contact interface area between the GOparticles and the solid phase, and provide more contact interface areabetween liquid and solid phases, possibly resulting in the augmentationof !_(SP) and drop of σ_(SL). Additionally, the filtration assemblyprocess may be a useful way to increase the density of the particles inthe suspension that approach the percolation threshold, to formcontinuous 3D porous network during the freeze-casting process.

In an exemplary method, as shown in FIGS. 6A-D and FIG. 24 thepre-reduced lamellar graphene oxide sheets 601, 602, 603, 604 graduallyconvert to partially reduced GO micro-gels during pre-reduction times of5 minutes, 10 minutes, 20 minutes and 30 minutes, respectively.

Vacuum filtration 103 is a common method for preparing graphene orgraphene-based films due to its easy manipulation. One of the advantagesof the filtration method is the convenience in controlling the thicknessand mass loading of an as-filtered film by adjusting the volume of thedispersion.

Per the exemplary method in FIG. 1, after the pre-reduced GO dispersionis filtered 103, the film is immersed into liquid nitrogen to solidifythe water molecule inside and between the micro gels, when, continuousice crystals may form and grow into the pre-reduced GO networks. Thepre-reduced GO sheets may be rejected from the advancing solidificationfront and collected between the gaps of growing ice crystals. Theframework may accommodate the 9% positive solidification volumeexpansion for liquid water changed to solidified ice crystal.

In some embodiments, freeze-casting may be a versatile, readilyaccessible and inexpensive solution-phase technique to controlcrystallization of a suspension and induce ordered hierarchical porousarchitectures. In some embodiments, freeze-casting is a phasesegregation process, wherein, as a liquid suspension freezes,spontaneous phase segregation gather the dispersed particles to thespace between the solvent crystals, and wherein subsequent sublimationof the solidified frozen solvent template under reduced pressure createsa three-dimensional network, where the pores become a replica of thesolvent crystals.

Directly freeze-casting a GO dispersion may only result in a randomlyoriented porous brittle monolith. A number of parameters, including thesize, shape, density and size distribution of the GO particles, mayaffect their interaction and reaction with the solution, which maymodify the solidification kinetics of the freezing procedure and theresulting pore structure. Only the fraction of GO particles insuspension may achieve a specific percolation threshold, and become“entrapped,” during the freezing process to form a continuous 3D porousnetwork. Therefore, the introduction of a pre-reduction step 102 toadjust the size, shape, and size distribution of the GO particles, and afiltration step 103 may increase the density of the dispersion capableof achieving the percolation threshold.

The morphology of the solidified ice crystal may largely dictate theporous characteristics of the final graphene films. Once completesolidification of hydro-film is achieved, pores may be created where theice crystals were. Finally, per the exemplary method, the subsequenthigher temperature long-term reduction may strengthen the connectionbetween pre-reduced GO gels and further increase the degree ofreduction.

The assembly of two-dimensional graphene sheets described herein, may beperformed using simple benchtop chemistry to form electrodes thatcomprise cellular graphene films which may be used in supercapacitorswithout the need for binders, a conductive additive required for theassembly of traditional supercapacitors.

The exemplary 3D porous RGO films described herein may satisfy the mainrequirements for high power density supercapacitor electrodes. The openand connected pores provide high-speed electrolyte ion transport andfreely accessible graphene surfaces for forming electrical doublelayers. The high electrical conductivity and robust mechanical strengthmay ensure high efficiency in exporting electrons to an outside load.Furthermore, these exemplary 3D porous RGO networks may be furtherscaled-up in their loading mass and/or thickness due to the controllablefiltration process.

Device Characteristics

FIGS. 7A-D show SEM images of the exemplary reduced GO 3D porousgraphene films 701, 702, 703, 704, which were pre-reduced for 5, 10, 20and 30 minutes respectively. FIGS. 8A-B show low and high magnificationSEM images of the exemplary reduced GO 3D porous graphene films,respectively, whereas the exemplary RGO films consists of stackedlamellar graphene sheets.

FIG. 10A presents a typical cross-section scanning electron microscope(SEM) image of an exemplary 3D porous RGO film 1001 under lowmagnification, which may exhibit a continuous open network with auniform thickness of about 12.6 μm. The honeycomb-like structures mayindicate that the pores are a replica of the ice crystals. As shown inthe high magnification SEM images in FIG. 10A-D, the pore sizes of theexemplary 3D porous RGO film 1001 are in the range of hundredsnanometers to several micrometers and the pore walls consist of thinlayers of graphene sheets, which is consistent with exemplarytransmission electron microscopy (TEM) results per FIG. 10E. Theexemplary TEM images, per FIGS. 10E and 10F, also reveal severalcrumpled 5-10 nm graphene sheets stacked on the surface of graphenewalls that are several tens of nanometers thick; possibly due torejection from the solidification front that pushes the dispersedpre-reduced GO sheets into the gaps between the ice crystals formedduring the freezing process. The exemplary clear lattice fringes, perFIGS. 10G and 10H, and the exemplary typical six-fold symmetrydiffraction pattern may provide further evidence for the nearly completereduction of the 3D porous RGO film 1001. The reduction process may beassociated with significant changes in the electrical properties of thefilm.

Exemplary supercapacitor devices with increased electrochemicalperformance were prepared by increasing the dispersion volume toincrease the loading mass. As seen in cross-sectional SEM images, perFIG. 9A-B, the exemplary as-prepared high loading mass films maymaintain their highly porous microstructure when the thickness isincreased to 20.4 μm, i.e. twice the loading, and to 44.7 μm, afive-fold increase in the loading.

The exemplary X-ray diffraction (XRD) pattern, per FIG. 13 of GO ischaracterized by a strong peak at 2θ=11.7°. The exemplary pre-reduced GOexhibits a significant decline in the intensity of the “GO” peak at10.8° and the development of a broad peak at 24° , which may indicatethe partial reduction of GO and the creation of extended graphenesheets. The XRD pattern of the exemplary 3D porous RGO film is comprisedmainly of a broad “graphene” peak, which suggests that a high degree ofreduction of the exemplary 3D porous RGO film has occurred. The XPSC_(1s) spectrum, per FIGS. 14A-C, confirms the exemplary results in FIG.13, wherein changes are observed in the peaks corresponding to oxygencontaining groups C and by the intensity ratio of the D and G peaks inRaman spectroscopy per FIG. 15.

FIGS. 17A-D present I-V conductivity tests of exemplary GO, pre-reducedGO and 3D porous RGO films. The exemplary GO film exhibits nonlinear andasymmetric behavior, with a differential conductivity value ranging fromx to y depending on the gate voltage. The exemplary pre-reduced GO filmsdisplay a more linear and symmetric I-V curve, with a stableconductivity of about 10.3 S/m. The I-V curve of the exemplary 3D porousRGO film is almost linear, which may be associated with a highconductivity of about 1,905 S/m. As such, the fabricated graphene filmsmay hold promise as high performance supercapacitor electrodes.

The cyclic voltammetry (CV) curves taken at scan rates from 0.2-20 V/sshown in FIG. 21A FIGS. 20A-D demonstrate that the exemplary 3D porousRGO electrodes retain their rectangular shape and high current densitieseven at an extremely high scan rate of 20 V/s. The rectangular nature ofthe CV curves may indicate a good electrical double-layer capacitor(EDLC) behavior for the exemplary 3D porous RGO films.

The CV curves, per FIGS. 19A-D, 20A-D, and 21B, and the galvanostaticcharge/discharge FIG. 23 curves may show a significant electrochemicalperformance enhancement for exemplary 3D porous RGO films, when comparedwith the exemplary RGO films. The more rectangular shape of the CVcurves, at a high scan rate of 1,000 mV/s, and more triangular shape ofthe galvanostatic charge/discharge curves, at a high current density of100 A/g, may indicate a better capacitive performance and electrolyteion transport of the exemplary 3D porous RGO electrode. The larger areaof the CV curve and the longer discharge time may also dictate a highercapacitance of the exemplary 3D porous RGO electrode. The high lineardependence (R2=0.9986) of the discharge current on the scan rate, up tohigh scan rates, may indicate an ultra-high power capability of theexemplary porous RGO electrode. The specific capacitance based on theactive materials of these two exemplary supercapacitor electrodes wasderived from the galvanostatic charge/discharge data and is summarizedin FIG. 21C.

Because of the high electrical conductivity and excellent ion transportinside the exemplary porous high loading mass films, the CV curves, perFIG. 22A, maintain their rectangular shapes even when the scan rate isincreased up to 1.0 V/s. The current density increases significantly asthe loading mass of the exemplary 3D porous RGO film is increased. As aresult, the gravimetric capacitance of the exemplary 3D porous RGO filmonly decreased by 6.6% (to 265.5 F/g) and 15% (to 241.5 F/g) at the massloadings of twice and five-fold, respectively, per FIG. 22B. Meanwhile,the areal capacitance increases from 56.8 mF/cm² to 109 mF/cm² and 246mF/cm², per FIG. 22C respectively.

The exemplary 3D porous RGO film exhibited an ultrahigh gravimetriccapacitance of about 284.2 F/g at a current density of about 1 A/g, andretained about 61.2% (173.8 F/g) of its initial capacitance when thecurrent density was increased up to 500 A/g. In contrast, the exemplaryRGO had a gravimetric capacitance of 181.3 F/g at 1 A/g and acapacitance retention of only 27.8% (50.4 F/g) at 500 A/g. FIG. 21Cdisplays the cycling stability of the exemplary electrodes during 10,000charge/discharge cycles at a current of 25 A/g. The exemplary 3D porousRGO films exhibited a capacitive retention of 97.6%, compared to the86.2% shown by the exemplary RGO films in FIG. 21D.

Furthermore, per FIG. 18, in spite of their highly porousmicrostructure, the as-prepared exemplary 3D porous RGO films exhibitedgood tensile strength of about 18.7 MPa, which is higher than previousreports for porous graphene films.

Calculation Methods

The capacitance of a supercapacitor (C_(cell)) in a two-electrode systemis calculated from its galvanostatic charge/discharge curves atdifferent current densities using:

C _(cell) =i _(discharge)/(dV/dt)

wherein i_(discharge) is the discharge current, t is the discharge time,the potential range of V is the voltage drop upon discharge excludingthe JR drop, and dV/dt is the slope of the discharge curve (in volts persecond, V/s).

Alternatively, C_(cell) may be calculated from CV curves by integratingthe discharge current (i) vs. potential (V) plots using the followingequation:

C_(cell) = ∫_(V_(min))^(V_(max))idV/Vv 

where i is the current in the negative CV curve, v is the scan rate, andV (V=V_(max)−V_(min)) represents the potential window.

Specific capacitances of single electrode active materials werecalculated based on their mass and area or volume. Since a symmetrictwo-electrode supercapacitor consists of two equivalent single-electrodecapacitors in series, the total capacitance of the two electrodes andthe capacitances of the positive and negative electrodes may becalculated using the equation below:

C_(positive) = C_(negative)$\frac{1}{C_{cell}} = {\frac{1}{C_{positive}} + \frac{1}{C_{negative}}}$

Thus C_(positive)=C_(negative)=2C_(cell)

In addition, the mass and volume of a single electrode accounts for halfof the total mass and volume of the two electrode system(M_(single-electrode)=1/2M_(two-electrode),V_(single-electrode)=1/2V_(two-electrode)). The area of a singleelectrode is equivalent to the area of the two-electrode system(S_(single-electrode)=S_(two-electrode)) with specific capacitances ofthe active material calculated according to the following equations:

$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{M_{{single}\mspace{14mu} {electrode}}} = {4\frac{C_{cell}}{M_{{two}\mspace{14mu} {electrode}}}}}$$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{S_{{single}\mspace{14mu} {electrode}}} = {2\frac{C_{cell}}{S_{{two}\mspace{14mu} {electrode}}}}}$$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{V_{{single}\mspace{14mu} {electrode}}} = {4\frac{C_{cell}}{V_{{two}\mspace{14mu} {electrode}}}}}$

Analogously, specific capacitances of the two-electrode system arecalculated based on the mass and area or volume of the two electrodesaccording to the following formulae:

$C_{{{two}\mspace{14mu} {electrodes}},M} = \frac{C_{cell}}{M_{{two}\mspace{14mu} {electrode}}}$$C_{{{two}\mspace{14mu} {electrodes}},S} = \frac{C_{cell}}{S_{{two}\mspace{14mu} {electrode}}}$$C_{{{two}\mspace{14mu} {electrodes}},V} = \frac{C_{cell}}{V_{{two}\mspace{14mu} {electrode}}}$

Thus,

C_(specific capacitance,M)=4 C_(two-electrode,M)

C_(specific capacitance,S)=2 C_(two-electrode,M)

C_(specific capacitance,V)=4 C_(two-electrode,V)

The specific energy densities of the electrode films based on the massand area or volume of the active materials were obtained from theequations:

E _(electrodes,x)=½C _(two electrodes,x)×(V−V _(IRdrop))²

where E_(electrode,x) and C_(two-electrode,x) represent the energydensities and specific capacitance of the two electrodes based ondifferent evaluating units (mass, area or volume), the V is thepotential window in volts, and V_(IRdrop) is the voltage IR drop at thebeginning of the discharge part of the galvanostatic charge/dischargecurves.

The energy density and power density based were calculated for the totalexemplary devices by normalizing by the total volume including the twoelectrodes, current collectors, electrolyte and separator. The powerdensities of the electrode materials based on different units werecalculated using the following equation:

$P_{{electrodes},x} = \frac{E_{{electrodes},x}}{t_{discharge}}$

where t_(discharge) is the discharge time from the galvanostatic curvesat different charge/discharge current densities.

As the calculations made herein are based on the power density obtainedby dividing the energy density by the discharging time, the notedexemplary power density values has actually been achieved. Some reporteddevice power densities are calculated from the square of the potentialwindow divided by 4 times the ESR, which is the theoretical idealmaximum power density of a supercapacitor. The actual highest powerdensity achieved by a supercapacitor is generally much lower than thisideal maximum value.

The specific capacitance of each exemplary devices was calculated bytaking into account the entire (mass, area or volume) of the stackeddevice. This includes the active materials, current collector,separator, and electrolyte. Thus, the specific capacitances of thedevice were calculated from the equations:

$C_{{device},M} = \frac{C_{cell}}{M_{device}}$$C_{{device},S} = \frac{C_{cell}}{S_{device}}$$C_{{device},V} = \frac{C_{cell}}{V_{device}}$

Therefore, the energy densities and power densities of the total devicewere calculated by the following equations:

$E_{{device},x} = {\frac{1}{2}C_{{device},x} \times \left( {V - V_{IRdrop}} \right)^{2}}$$C_{{device},x} = \frac{E_{{device},x}}{t_{discharge}}$

As summarized in a Ragone plot, per FIG. 22D, the exemplary 3D porousRGO supercapacitors exhibits high power densities of about (7.8-14.3kW/kg). Furthermore, by increasing the mass loading of the activematerials, the exemplary 3D porous RGO supercapacitor may store a highenergy density up to 1.11 Wh/L, which is comparable to supercapacitorsbased on organic electrolytes or ionic liquids.

The schematic illustration presented in FIG. 3 displays a Randlescircuit of the exemplary device. In some embodiments, a Randles circuitis an equivalent electrical circuit that consists of an activeelectrolyte resistance RS in series with the parallel combination of thedouble-layer capacitance and an impedance of a faradaic reaction. ARandles circuit is commonly used in Electrochemical ImpedanceSpectroscopy (EIS) for interpretation of impedance spectra.

Electrochemical impedance spectroscopy (EIS), alternatively namedimpedance spectroscopy or dielectric spectroscopy, is an experimentalmethod of characterizing the energy storage and dissipation propertiesof electrochemical systems. EIS measures the impedance of a system as afunction of frequency, based on the interaction of an external fieldwith the electric dipole moment of the sample, often expressed bypermittivity. Data obtained by EIS may be expressed graphically in Bodeor Nyquist plots.

The measured Nyquist plots were fit on the basis of an equivalentRandles circuit in FIG. 3 by using the following equation:

$Z = {R_{s} + \frac{1}{{j\; \omega \; C_{dl}} + {1/R_{ct}} + W_{o}} + \frac{1}{{1j\; \omega \; C_{l}} + {1/R_{leak}}}}$

where R_(s) is the cell internal resistance, C_(dl) is the double layercapacitance, R_(ct) is the charge transfer resistance, W_(o) is theWarburg element, C₁ is the low frequency mass capacitance, and R_(leak)is the low frequency leakage resistance. These resistor and capacitorelements in the equivalent circuit may be related to specific parts inthe Nyquist plot. At high frequency, the point of intersection on thereal axis represents the internal resistance R_(s), which includes theintrinsic electronic resistance of the electrode material, the ohmicresistance of the electrolyte, and the interfacial resistance betweenthe electrode and the current collector. The semicircular in the highfrequency region provides the behavior of the interfacial chargetransfer resistance R_(ct) and the double layer capacitance C_(dl).After the semicircle, the exemplary Nyquist plot exhibits a straightlong tail almost perpendicular to the x-axis and stretching to the lowfrequency region. This vertical line may represent the mass capacitanceC1, and the inclined angle suggests a resistive element, which is theleakage resistance R_(leak). The transmission line with an angle ofnearly 45 degrees to the x-axis from high frequency to the mid frequencymay represent the Warburg element Wo, which is expressed as:

$W_{ox} = \frac{A}{j\; \omega^{n}}$

Where A is the Warburg coefficient, w is the angular frequency, and n isthe constant phase element. Exponent Electrochemical ImpedanceSpectroscopy (EIS) may be a very useful method to analyze electrolyteion transport and other electrochemical behavior. FIG. 21E shows thecomparison of the Nyquist plots of the exemplary 3D porous RGO film andthe exemplary RGO film electrodes. The Nyquist plot of the exemplary 3Dporous RGO film features a nearly vertical curve, possibly indicating agood capacitive performance. A close-up observation of the highfrequency regime reveals a semicircle with a ˜45° Warburg region. TheNyquist plot of the exemplary 3D porous RGO electrode shows a shorterWarburg region and a smaller semicircle, which may indicate a lowercharge transfer resistance and a more efficient electrolyte iondiffusion, when compared to the exemplary RGO electrode. The Nyquistplots are fitted to an equivalent circuit per FIG. 3. The internalresistances (Rs) are about 0.202Ω and about 0.244Ω; with chargetransport resistances (Rct) of about 0.181Ω and about 1.04Ω obtained byfitting the exemplary 3D porous RGO film and exemplary RGO filmsupercapacitors, respectively. These low resistance values may indicatea high electron conductivity along the graphene walls, and a high-speedion migration through the 3D open pores. The open surfaces of the 3Dporous RGO films may be easily accessed by electrolyte ions without adiffusion limit, which may guarantee a large capacitance at high currentdensity/scan rate. In contrast, the condensed layer structure of RGOfilms may only provide a narrow neck-like channel and confined pores forelectrolyte ion transport, which may result in increased resistance andreduced capacitances. The exemplary Bode plots per FIG. 21F display acharacteristic frequency f_(o) at the phase angle of −45°, which marksthe transition point from resistive behavior to capacitive behavior. Theexemplary 3D porous RGO supercapacitor exhibits an f_(o) of about 55.7Hz, which corresponds to a time constant (τ0=1/f0) of 17.8 ms, which issignificantly lower than 91.7 ms exhibited by the exemplary RGOsupercapacitor. This time constant for the exemplary 3D porous RGOsupercapacitor is lower than some pure carbon basedmicro-supercapacitors (e.g. 26 ms) for onion-like carbon, and 700 ms foractivated carbon. This extremely low time constant may provide furtherevidence for the high-speed ion diffusion and transport inside the 3Dporous RGO electrodes. The sum of Rs and Rct may be the chiefcontributors to the equivalent series resistance (ESR), which mainlylimits the specific power density of a supercapacitor. Thus, the lowESR, high capacitance and nearly ideal electrolyte ion transport of theexemplary 3D porous RGO electrodes provide the extremely high powerdensity of 282 kW/kg and high energy density of 9.9 Wh/kg, even withonly a 1.0 V potential window using an aqueous electrolyte. This highpower density from the exemplary 3D porous RGO supercapacitor is closeto that of an aluminum electrolytic capacitor and much higher than mostpreviously reported EDLCs, pseudo-capacitors, and even asymmetricsupercapacitors.

Exemplary Measurement Devices

The morphology and microstructure of the exemplary prepared films werecharacterized using a field emission scanning electron microscope(FE-SEM, JEOL 6701F) and a transmission electron microscopy (TEM, FEITF20). X-ray diffraction patterns were collected using a PanalyticalX'Pert Pro X-ray Powder Diffractometer with Cu-Ka radiation (/c=1.54184A). Exemplary Raman spectroscopy measurements were performed using alaser micro-Raman system (Renishaw) at an excitation wavelength of 633nm. Atomic force microscopy images were recorded using a scanning probemicroscope (Bruker Dimension 5000). The tensile strength of the eachfilm was tested by a tensile testing machine (Q800 DMA (DynamicMechanical Analyzer)). X-ray photoelectron spectroscopy data wascollected with a spectrometer (Kratos AXIS Ultra DLD) using amonochromatic AlKa X-ray source (hv 1486.6 eV).

All the electrochemical experiments were carried out using atwo-electrode, per FIG. 16, system with a potentiostat (Bio-Logic VMP3).The EIS measurements were performed at open circuit potential with asinusoidal signal over a frequency range from 1 MHz to 10 MHz at anamplitude of 10 mV. The cycle life tests were conducted by galvanostaticcharge/discharge measurements.

The devices described herein can alternatively be measured,characterized and tested by any alternative equivalent means, devicesand equipment.

Terms and Definitions

Unless otherwise defined, all technical terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs. As used in this specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. Any referenceto “or” herein is intended to encompass “and/or” unless otherwisestated.

As used herein, and unless otherwise specified, the term GO refers tographene oxide.

As used herein, and unless otherwise specified, the term RGO refers toreduced graphene oxide.

As used herein, and unless otherwise specified, the term 3D refers tothree dimensional.

As used herein, and unless otherwise specified, the term SEM refers to ascanning electron microscope.

As used herein, and unless otherwise specified, the term TEM refers to atransmission electron microscope.

As used herein, and unless otherwise specified, the term AFM refers toan atomic-force microscope.

As used herein, and unless otherwise specified, CV chart refers to acyclic voltammogram chart.

As used herein, and unless otherwise specified, EIS refers toelectrochemical impedance spectroscopy.

As used herein, and unless otherwise specified, EDLC refers toelectrical double-layer capacitor.

As used herein, and unless otherwise specified, XRD refers to X-RayPower Diffraction.

As used herein, and unless otherwise specified, XPS refers to X-RayPhotoelectric Spectroscopy.

While preferable embodiments of the present invention have been shownand described herein, it will be obvious to those skilled in the artthat such embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

As used herein, and unless otherwise specified, the term “about” or“approximately” means an acceptable error for a particular value asdetermined by one of ordinary skill in the art, which depends in part onhow the value is measured or determined. In certain embodiments, theterm “about” or “approximately” means within 1, 2, 3, or 4 standarddeviations. In certain embodiments, the term “about” or “approximately”means within 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%,1%, 0.5%, 0.1%, or 0.05% of a given value or range. In certainembodiments, the term “about” or “approximately” means within 40.0grams, 30.0 grams, 20.0 grams, 10.0 grams, 5.0 grams, 1.0 grams, 0.9grams, 0.8 grams, 0.7 grams, 0.6 grams, 0.5 grams, 0.4 grams, 0.3 grams,0.2 grams or 0.1 grams, 0.05 grams, 0.01 grams of a given value orrange. In certain embodiments, the term “about” or “approximately” meanswithin 60 F/g, 50 F/g, 40 F/g, 30 F/g, 20 F/g, 10 F/g, 9 F/g, F/g, 8F/g, 7 F/g, 6 F/g, 5 F/g, 4 F/g, 3 F/g, 2 F/g, 1 F/g of a given value orrange. In certain embodiments, the term “about” or “approximately” meanswithin 30.0 A/g, 20.0 A/g, 10.0A/g 5.0 A/g 1.0 A/g, 0.9 A/g, 0.8 A/g,0.7 A/g, 0.6 A/g, 0.5 A/g, 0.4 A/g, 0.3 A/g, 0.2 A/g or 0.1 A/g of agiven value or range. In certain embodiments, the term “about” or“approximately” means within 20 kW/kg, 15 kW/kg, 10 kW/kg, 9 kW/kg, 8kW/kg, 7 kW/kg, 6 kW/kg, 5 kW/kg, 4 kW/kg, 3 kW/kg, 2 kW/kg, 1 kW/kg,0.5 kW/kg, 0.1 kW/kg, or 0.05 kW/kg of a given value or range. Incertain embodiments, the term “about” or “approximately” means within20Wh/kg, 15Wh/kg, 10Wh/kg, 9Wh/kg, 8Wh/kg, 7Wh/kg, 6Wh/kg, 5Wh/kg,4Wh/kg, 3Wh/kg, 2Wh/kg, 1Wh/kg, 0.5Wh/kg, 0.1Wh/kg, or 0.05Wh/kg of agiven value or range. In certain embodiments, the term “about” or“approximately” means within 5V, 4V, 3V, 2V, 1V, 0.5V, 0.1V, or 0.05V ofa given value or range. In certain embodiments, the term “about” or“approximately” means within 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm,40 nm, 30 nm, 20 nm, 10 nm, 9 nm, nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3nm, 2 nm, 1 nm of a given value or range. In certain embodiments, theterm “about” or “approximately” means within 40° C., 30° C., 20° C., 10°C., 9° C., ° C., 8° C., 7° C., 6° C., 5° C., 4° C., 3° C., 2° C., 1° C.of a given value or range. In certain embodiments, the term “about” or“approximately” means within 50 minutes, 60 minutes, 40 minutes, 30minutes, 20 minutes, 10 minutes, 9 minutes, minutes, 8 minutes, 7minutes, 6 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, 1minutes of a given value or range. In certain embodiments, the term“about” or “approximately” means within 50 hours, 60 hours, 40 hours, 30hours, 20 hours, 10 hours, 9 hours, hours, 8 hours, 7 hours, 6 hours, 5hours, 4 hours, 3 hours, 2 hours, 1 hours of a given value or range. Incertain embodiments, the term “about” or “approximately” means within 5L, 4 L, 3 L, 2 L, 1 L, 0.5 L, 0.1 L, or 0.05 L. In certain embodiments,the term “about” or “approximately” means within 5 cm², 4 cm², 3 cm², 2cm², 1 cm², 0.5 cm², 0.1 cm², or 0.05 cm². In certain embodiments, theterm “about” or “approximately” Means within 5 M, 4 M, 3 M, 2 M, 1 M,0.5 M, 0.1 M, or 0.05 M of a given value or range.

Other Non-limiting Embodiments

Ever since the discovery of graphene a decade ago, researchers haveproposed dozens of potential uses, from faster computer chips andflexible touchscreens to hyperefficient solar cells and desalinationmembranes. One exciting application that has sparked significantinterest is the ability of graphene to store electrical charge. A singlesheet of graphene sufficient in size to cover an entire soccer fieldwould weigh only about 6 grams. This huge surface area associated withthis small amount of graphene can be squeezed inside an AA size battery,enabling new energy storage devices with the ability to store massiveamounts of charge. However, current three-dimensional (3D) graphenefilms suffer from poor electrical conductivity, weak mechanicalstrength, and chaotic porosity.

The inventors have recognized a need and have provided solutions todevelop new methods for the preparation and processing of graphene intoelectrodes with controlled porosity and high surface area for use in avariety of applications.

The present disclosure relates to an approach for the fabrication ofthree-dimensional (3D) hierarchical porous films through filtrationassembly of partially reduced graphene oxide and a subsequentfreeze-casting process. This fabrication process provides an effectivemeans for controlling the pore size, electronic conductivity, andloading mass of the electrode materials and provides an opportunity fordesigning devices with high energy density. These outstanding propertiesresult in supercapacitors with a power density in excess of 280 kW/kg,which is among the highest values reported thus far.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description in association with the accompanyingdrawings.

The present disclosure relates to an approach for the fabrication ofthree-dimensional (3D) hierarchical porous films through filtrationassembly of partially reduced graphene oxide and a subsequentfreeze-casting process. This fabrication process provides an effectivemeans for controlling the pore size, electronic conductivity, andloading mass of the electrode materials and provides an opportunity fordesigning devices with high energy density. These outstanding propertiesresult in supercapacitors with a power density in excess of 280 kW/kg,which is among the highest values reported thus far.

Electrochemical capacitors, also known as supercapacitors, are energystorage devices like batteries, yet they can be recharged a hundred to athousand times faster. Their high power density and excellentlow-temperature performance have made them the technology of choice forback-up power, cold starting, flash cameras, and regenerative braking.They also play an important role in the progress of hybrid and electricvehicles. With all the progress in the past decades, commercialsupercapacitors currently provide a power densities below 10 kW/kg. Wehave developed supercapacitors using cellular graphene films that arecapable of providing power densities in excess of 280 kW/kg. Thistremendous improvement in the power density of graphene supercapacitorsenables them to compete not only with the existing supercapacitortechnology but also with batteries and capacitors in a large number ofapplications. In addition, we envision these 3D porous films to beuseful in a broad range of applications, including energy conversion andstorage (e.g., capacitors and/or batteries), catalysis, sensing,environmental remediation, and scaffolds for electronic and medicalapplications.

Other possible, non-limiting applications for cellular 3D graphene arethe following: Portable electronics: cell phones, computers, cameras.Medical devices: life-sustaining and life-enhancing medical devices,including pacemakers, defibrillators, hearing aids, pain managementdevices, and drug pumps. Electric vehicles: High-power batteries withlong lifetime are needed to improve the electric vehicles industry.Space: Cellular graphene supercapacitors can be used in space to powerspace systems including rovers, landers, spacesuits, and electronicequipment. Military batteries: The military uses special batteries forpowering a huge number of electronics and equipment. Of course, reducedmass/volume is highly preferred. Electric aircraft: an aircraft thatruns on electric motors rather than internal combustion engines, withelectricity coming from solar cells or batteries. Grid-scale energystorage: Batteries are widely used to store electrical energy duringtimes when production (from power plants) exceeds consumption, and thestored energy is used at times when consumption exceeds production.Renewable energy: Since the sun does not shine at night and the winddoes not blow at all times, batteries have found their way tooff-the-grid power systems to store excess electricity from renewableenergy sources for use during hours after sunset and when the wind isnot blowing. Of course, high-power batteries can harvest energy fromsolar cells with higher efficiency than the current state-of-the-artbatteries. Power tools: Cellular 30 graphene supercapacitors wouldenable fast-charging cordless power tools such as drills, screwdrivers,saws, wrenches, and grinders. The trouble with current batteries is longrecharging time. Batteries, including lithium ion batteries: In certainapplications, supercapacitors may in some cases be used instead of, orin combination with, batteries.

The state-of-the-art supercapacitors use electrodes made of activatedcarbons that are limited by complex microporous structure, which limitstheir power density. The technology based on activated carbon has beenin use over the past 40 years, and the maximum power density is stilllimited at 10 kW/kg. The assembly of two-dimensional graphene sheetsusing simple benchtop chemistry results in cellular graphene films thatcan be directly used in supercapacitors without the need for binders, aconductive additive required for the assembly of traditionalsupercapacitors. These films demonstrate ultrahigh power and very fastfrequency response (about 0.017 seconds compared with ˜1 second forcommercial technology). The present disclosure further providesadvantages over conventional capacitors in the following aspects: Theprocess described in the present disclosure is an improvement lendingitself to more efficient scale up. The power density achieved with thegraphene films (>280 kW/kg) is much higher than previously reported withother forms of graphene.

Those skilled in the art will recognize improvements and modificationsto the present disclosure. All such improvements and modifications areconsidered within the scope of the concepts disclosed herein.

GO was prepared from natural graphite flakes by a modified Hummers'method, as previously described. In a typical procedure, as-synthesizedGO was suspended in water to give a homogeneous aqueous dispersion witha concentration of 3 mg m1-1. Then 1 ml of GO dispersion was mixed with7 mg ascorbic acid in a 20 ml cylindrical glass vial. After beingvigorously shaken for a few minutes, the mixture was then placed in a50° C. oven for 5 to 50 minutes to obtain different degrees ofreduction, i.e. partially reduced GO. The partially reduced GOdispersion was next vacuum filtered through a cellulose membrane (0.22μm pore size). The vacuum was disconnected immediately once no freedispersion was left on the filter paper. Both the filter membrane andpartially reduced GO film were vertically immersed into a liquidnitrogen bath to freeze them for 30 minutes. After being thawed at roomtemperature, the film was transferred into a cylindrical glass vial andplaced in a 100° C. oven overnight to obtain further reduction. The 3Dporous RGO films were then transferred to a Petri dish and immersed indeionized water for one day to remove any remaining ascorbic acid.Thicker 3D porous RGO films were prepared by simply increasing theamount of GO to 2 or 5 ml and ascorbic acid to 14 or 35 mg. Thethickness of the 3D porous RGO films, as measured from cross-sectionalSEM images, were found to be ˜12.6, 20.4 and 44.7 μm, respectively. Theareal loading mass of the 3D porous RGO films are ˜0.2, 0.41 and 1.02 mgcm-2, respectively. As a control, chemically reduced graphene film wasfabricated by vacuum filtering chemically reduced GO sheets. The loadingmass and the thickness of this RGO is ˜0.2 mg cm-2 and ˜2.1 μm,respectively.

Fabrication of 3D porous RGO- and RGO-supercapacitors. 3D porous RGO andRGO films were cut into 1 cm×1 cm square pieces and then carefullypeeled off from the filter membrane. Next, the freestanding electrodefilms were immersed into 1.0 M H2SO4 aqueous electrolyte overnight toexchange their interior water with electrolyte. Subsequently, the 3Dporous RGO film slices were placed onto platinum foils. Two similar 3Dporous RGO films on separate metal foils were directly used aselectrodes without adding any other additives or further treatments.These two electrodes were separated by an ion-porous separator(polypropylene membrane, NKK MPF30AC100) and assembled into a sandwicharchitecture supercapacitor and tightly sealed with Kapton tape.

The morphology and microstructure of the prepared films wereinvestigated by means of field emission scanning electron microscopy(FE-SEM, JEOL 6701F) and transmission electron microscopy (TEM, FEITF20). X-ray diffraction patterns were collected on a Panalytical X'PertPro X-ray Powder Diffractometer with Cu-Kα radiation (λ=1.54184 Å).Raman spectroscopy measurements were performed using a Renishaw Vialaser micro-Raman system (Renishaw) at an excitation wavelength of 633nm. Atomic force microscopy images were recorded using a BrukerDimension 5000 Scanning Probe Microscope in tapping mode (BrukerDimension 5000). Tensile strength of the each film was tested on atensile testing machine (Q800 DMA (Dynamic Mechanical Analyzer)). X-rayphotoelectron spectroscopy data were collected with a Kratos AXIS UltraDLD spectrometer using a monochromatic A1Kα X-ray source (hv=1486.6 eV).

All the electrochemical experiments were carried out using atwo-electrode system with a Bio-Logic VMP3 potentiostat. The EISmeasurements were performed at open circuit potential with a sinusoidalsignal over a frequency range from 1 MHz to 10 MHz at an amplitude of 10mV. The cycle life tests were conducted by galvanostaticcharge/discharge measurements. Calculations of the specific capacitanceand the energy and power densities are discussed in detail in thefollowing sections.

Despite the impressive developments achieved during the last decade inthe field of supercapacitor research, inconsistent calculations have ledto misunderstandings and make comparing results from different researchgroups difficult. Thus, here we carefully illustrate in detail ourcalculation methods for determining the different parameters needed forevaluating the performance of the supercapacitors.

The capacitance of a supercapacitor (Ccell) in a two-electrode systemwas calculated from its galvanostatic charge/discharge curves atdifferent current densities using:

C _(cell) =i _(discharge)/(dV/dt)

wherein i_(discharge) is the discharge current, t is the discharge time,the potential range of V is the voltage drop upon discharge excludingthe JR drop, and dV/dt is the slope of the discharge curve (in volts persecond, V/s).

Alternatively, C_(cell) may be calculated from CV curves by integratingthe discharge current (i) vs. potential (V) plots using the followingequation:

C_(cell) = ∫_(V_(min))^(V_(max))idV/Vv 

where i is the current in the negative CV curve, v is the scan rate, andV (V=V_(max)−V_(min)) represents the potential window.

Specific capacitances of single electrode active materials werecalculated based on their mass and area or volume. Since a symmetrictwo-electrode supercapacitor consists of two equivalent single-electrodecapacitors in series, the total capacitance of the two electrodes andthe capacitances of the positive and negative electrodes may becalculated using the equation below:

C_(positive) = C_(negative)$\frac{1}{C_{cell}} = {\frac{1}{C_{positive}} + \frac{1}{C_{negative}}}$

Thus C_(positive)=C_(negative)=2C_(cell).

In addition, the mass and volume of a single electrode accounts for halfof the total mass and volume of the two electrode system(M_(single-electrode)=1/2M_(two-electrode),V_(single-electrode)=1/2V_(two-electrode)). The area of a singleelectrode is equivalent to the area of the two-electrode system(Ssingle-electrode=S_(two-electrode)) with specific capacitances of theactive material calculated according to the following equations:

$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{M_{{single}\mspace{14mu} {electrode}}} = {4\frac{C_{cell}}{M_{{two}\mspace{14mu} {electrode}}}}}$$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{S_{{single}\mspace{14mu} {electrode}}} = {2\frac{C_{cell}}{S_{{two}\mspace{14mu} {electrode}}}}}$$C_{{{specific}\mspace{14mu} {capacitance}},M} = {\frac{C_{{single}\mspace{14mu} {electrode}}}{V_{{single}\mspace{14mu} {electrode}}} = {4\frac{C_{cell}}{V_{{two}\mspace{14mu} {electrode}}}}}$

Analogously, specific capacitances of the two-electrode system arecalculated based on the mass and area or volume of the two electrodesaccording to the following formulae:

$C_{{{two}\mspace{14mu} {electrodes}},M} = \frac{C_{cell}}{M_{{two}\mspace{14mu} {electrode}}}$$C_{{{two}\mspace{14mu} {electrodes}},S} = \frac{C_{cell}}{S_{{two}\mspace{14mu} {electrode}}}$$C_{{{two}\mspace{14mu} {electrodes}},V} = \frac{C_{cell}}{V_{{two}\mspace{14mu} {electrode}}}$

Thus,

C_(specific capacitance,M)=4 C_(two-electrode,M)

C_(specific capacitance,S)=2 C_(two-electrode,M)

C_(specific capacitance,V)=4 C_(two-electrode,V)

Therefore, the energy densities and power densities of the total devicewere calculated by the following equations:

$E_{{device},x} = {\frac{1}{2}C_{{device},x} \times \left( {V - V_{IRdrop}} \right)^{2}}$$C_{{device},x} = \frac{E_{{device},x}}{t_{discharge}}$

The measured Nyquist plots was well fit on the basis of an equivalentRandles circuit in FIG. 3 by using the following equation:

$Z = {R_{s} + \frac{1}{{j\; \omega \; C_{dl}} + {1/R_{ct}} + W_{o}} + \frac{1}{{1j\; \omega \; C_{l}} + {1/R_{leak}}}}$

where Rs is the cell internal resistance, Cdl is the double layercapacitance, Rct is the charge transfer resistance, Wo is the Warburgelement, Cl is the low frequency mass capacitance, and Rleak is the lowfrequency leakage resistance. As illustrated in FIG. 3, these resistorand capacitor elements in the equivalent circuit are related to specificparts in the Nyquist plot. At high frequency, the point of intersectionon the real axis represents the internal resistance Rs, which includesthe intrinsic electronic resistance of the electrode material, the ohmicresistance of the electrolyte, and the interfacial resistance betweenthe electrode and the current collector. The semicircular in the highfrequency region provides the behavior of the interfacial chargetransfer resistance Rct and the double layer capacitance Cdl. After thesemicircle, the Nyquist plot exhibits a straight long tail almostperpendicular to the x-axis and stretching to the low frequency region.This almost ideal vertical line represents the mass capacitance Cl, andthe inclined angle suggests a resistive element, which is the leakageresistance Rleak. The transmission line with an angle of nearly 45degrees to the x-axis from high frequency to the mid-frequencyrepresents the Warburg element Wo, which is expressed as:

$W_{ox} = \frac{A}{j\; \omega^{n}}$

Where A is the Warburg coefficient, ω is the angular frequency, and n isan exponent.

Building three-dimensional porous microstructures is an effective way tomake use of the extraordinary nanoscale properties of individualgraphene sheets. However, current 3D graphene films suffer from poorelectrical conductivity, weak mechanical strength, and chaotic porosity.Here, we demonstrate a method combining freeze-casting and filtration tosynthesize 3D reduced graphene oxide (RGO) films with open porosity,high electrical conductivity (>1900 S m-1), and good tensile strength(18.7 MPa). Taking advantage of the abundant interconnected pathways forelectrolyte/ion transport, the resulting supercapacitors based on the 3Dporous RGO film exhibit extremely high specific power densities (>280 kWkg-1) and high energy densities (up to 9.9 Wh kg-1) in aqueouselectrolyte. The fabrication process provides an effective means forcontrolling the pore size, electronic conductivity and loading mass ofthe electrode materials, providing an opportunity for designing deviceswith high energy density. We envision these 3D porous films to be usefulin a broad range of applications including energy conversion andstorage, catalysis, sensing and environmental remediation.

Due to the large fluctuations in electricity generation from renewablesources, energy storage devices with high power density are urgentlyneeded for storing energy and supplying electricity on demand.Electrochemical capacitors, known as supercapacitors, have attracted agreat deal of attention because of their high power densities, long lifespans and fast charging capabilities. Supercapacitors can provide powerdensity in excess of 10 kW kg-1, which is 10 times larger than currentlypossible with lithium-ion batteries. They are ideal energy storagecandidates in applications where high power densities are needed such asfor energy recapture and delivery in hybrid vehicles, electric vehicles,smart grids, and backup power for electric utilities and factories.Unlike batteries that are limited by slow chemical reactions,supercapacitors store charge through highly reversible ion adsorption orfast redox reactions, which enables fast energy capture and delivery.

Recently, significant research efforts have focused on increasing energydensities of supercapacitors. Unfortunately, these energy densityenhancements usually come at the cost of losses in power or cyclingcapability, which are the most important characteristics ofsupercapacitors. Without high power density and long cycling capability,supercapacitors are reduced to mediocre battery-like energy storagedevices. In practice, high power supercapacitors are desirable fornumerous applications, including heavy-duty loading applications,harvesting regenerative braking energy, and load leveling in a smartelectric grid. In these situations, a large amount of energy needs to beeither stored or delivered in high power density energy storage devices.Therefore, high power density is still an essential property for thepractical applications of supercapacitors.

The electrode material is the central component of supercapacitors andlargely dictates their ultimate energy storage performances. Owing toits extraordinary properties, such as high electrical conductivity aswell as high specific surface area, and a wide stable potential window,graphene, a one atom-thin two-dimensional flake of carbon, holds greatpromise as a high performance electrode material for supercapacitors.

Graphene film, often called graphene paper, is an important macroscopicstructure of graphene. A number of methods, such as blade-coating,spray-coating, layer-by-layer assembly, interfacial self-assembly andfiltration assembly have been developed to fabricate graphene films.However, due to the shear stress, interfacial tension or vacuumcompression during the fabrication process, the two-dimensional (2D)layered graphene sheets can easily restack to form dense lamellarmicrostructures, which lose most of the surface area of the originalgraphene sheets. Recently, Li and coworkers demonstrated that thepresence of a nonvolatile liquid electrolyte that can serve as aneffective “spacer” to prevent the irreversible π-π stacking betweengraphene sheets. However, these fabricated dense layered graphene filmslack sufficient open hierarchical pores, which serve as ion-bufferingreservoirs and high speed ion transport channels for effectiveelectrochemical kinetic processes. The presence of these hierarchicalpores is a critical factor for obtaining high power densities and shortcharging times. Therefore, it is important to fabricate graphene filmelectrodes with continuous hierarchical pores, especially to achievehigh power density supercapacitors.

Here we demonstrate that 3D hierarchical porous graphene films can bereadily fabricated by filtration assembly of partially reduced grapheneoxide and a subsequent freeze-casting process. The resulting porousgraphene films exhibit a combination of useful properties including:good electrical conductivity, high mechanical strength and extreme highperformance in supercapacitors. Furthermore, this new 3D porous graphenefilm is not only useful in supercapacitors, but also has promisingpotential in broad applications, such as sensors, catalysis, batteries,gas absorption, hydrogen storage, and scaffolds for electronic andmedical applications.

Among various methods developed for the fabrication of porous materials,freeze-casting has attracted considerable attention recently, as it is aversatile, readily accessible and inexpensive solution-phase techniquethat can employ the controlled crystallization of a suspension to induceordered hierarchical porous architectures.

Generally, the freeze-casting technique is a phase segregation process.As a liquid suspension freezes, spontaneous phase segregation gathersthe dispersed particles to the space between the solvent crystals,followed by sublimation of the solidified frozen solvent template fromthe solid to the gas phase under reduced pressure. This creates athree-dimensional network, where the pores become a replica of thesolvent crystals.

To date, freeze-casting has been adopted to introduce high porosity intoa variety of compact materials, endowing them several novel propertiesand opening up the possibility for new applications. For example,cellular ceramics have been formed that are useful as light-weightinsulators or filters, which can withstand high temperatures and exhibithigh compressive strength. Additionally, polymers with or withoutinorganic nano-fillers (e.g. carbon nanotubes or clay) have been createdas tissue engineering substrates or scaffolds for energy storageelectrodes. Due to these previous results, the variety of materialssuccessfully processed by this technique suggests that the underlyingprinciples dictating the porous structure formation mechanisms rely onphysical parameters, morphology of the “particles” and the interactionswith solutions rather than the chemical properties.

Graphene oxide (GO), can be produced in bulk from graphite at low cost,as a precursor to fabricate porous graphene films. The diameters of theGO sheets are in the range of several micrometers, with a typicalthickness of approximately 1.2 nm. According to a literature report, thethickness of a GO monolayer is approximately 1-1.4 nm, which is thickerthan an ideal monolayer of graphene (thickness ˜0.34 nm), due to thepresence of functional groups and adsorbed molecules. Since thefunctional groups make GO strongly hydrophilic and negatively charged,the single layer GO sheets can be homogeneously dispersed in an aqueoussolution. However, if one directly freeze-casts a GO dispersion, it willonly result in a randomly oriented porous brittle monolith. A number ofparameters, including the size and density of the “particles”, theirsize distribution, and their shape, will affect the interactions betweenthe “particles” and solution, which results in modifying thesolidification kinetics of the freezing procedure and the resulting porestructure. Only the fraction of “particles” in suspension achieved up toa specific percolation threshold, known as the entrapped “particles”during the freezing process, can form a continuous 3D porous network.Therefore, we introduce pre-reduction and control the reduction time toadjust the size, shape, and size distribution and carry out filtrationassembly to increase the density of the dispersion to achieve thepercolation threshold.

The lamellar graphene oxide sheets gradually grow up to partiallyreduced GO micro-gels when pre-reduction time increase from 5 up to 30minutes. Then we process all these pre-reduced GO samples with the sameprocedures show in the FIG. 1 until we got graphene films. Afterfiltering these pre-reduced GO dispersion, we drop the film into liquidNitrogen to solidify the water molecule inside and between the microgels. Under ideal conditions, continuous ice crystals are formed andgrow into the pre-reduced GO networks. The pre-reduced GO sheetsrejected from the advancing solidification front and collected betweenthe gaps of growing ice crystals. The framework should also accommodatethe 9% positive solidification volume expansion for liquid water changedto solidified ice crystal. The morphology of the solidified ice crystalwill largely dictate the porous characteristics of the final graphenefilms. Once complete solidification of hydro-film is achieved, theporosity is created where the ice crystals were. Then, the subsequenthigher temperature long-term reduction is to strengthen the connectionbetween pre-reduced GO gels and further increase the degree ofreduction.

After series of comparable experiments, we found that only the 30minutes pre-reduced sample can be assembled into the ideal 3D porousgraphene film. According to the mechanism of forming porosity by freezecasting, we conclude two main reasons for necessity of the pre-reductionto form the porosity of the graphene films. First, the 3D micro-gelstructures effectively resist the aggregation of the graphene oxidesheets during the filtration assembly and leave sufficient space for thesolidification of water. In contrast, the compact configuration offiltered 2D GO sheets jam the redistribution during freezing procedure.Second, during the growth of GO sheets to micro-gels, the particle sizewas increasing and the 2D lamellar sheets were changing to 3D micronetworks. In order to assemble to integral porous graphene film, the“particles” in suspension must be rejected from the advancingsolidification front in freezing procedure. The thermodynamic conditionfor a “particle” to be rejected by the solidification front is that theinterfacial free energies satisfying this following criterion:

Δσ=Δσ_(SP)−(Δσ_(LP)+Δσ_(SL))>0

where σ_(SP), σ_(LP), and σ_(SL) are the interfacial free energiesassociated with the solid (ice)-particle (pre-reduced GO micro-gel or GOsheets), liquid (water)-particle and solid-liquid interfacerespectively.

The size increase and morphology change decrease the contact interfacearea between the “particles” and solid phase and provide more contactinterface area between liquid and solid phases, which result in theaugment of σ_(SP) and drop of σ_(SL). This makes the pre-reduced GOmicro-gel system more tend to satisfy the pre-mentioned criterion. Inaddition, the filtration assembly process is a useful way to increasethe density of the particles in the suspension to approach thepercolation threshold, which is another critical condition for formingcontinuous 3D porous network during the freeze-casting process.

The X-ray diffraction (XRD) pattern of GO is characterized by a strongpeak at 2θ=11.7°. Pre-reduced GO exhibits a significant decline in theintensity of the “GO” peak at 10.8° while a broad peak develops at 24°,which indicates the partially reduction of GO, and the creation ofextended graphene sheets. After completion of the reduction process, theXRD pattern only shows a broad “graphene” peak, which suggests that ahigh degree of reduction of the 3D porous RGO films has occurred. TheXPS C_(1s) spectrum where changes are observed in the peakscorresponding to oxygen containing groups and 2. The intensity ratio ofthe D and G peaks in Raman spectroscopy.

A typical cross-section scanning electron microscope (SEM) image of a 3Dporous RGO film under low magnification, exhibits a continuous opennetwork with a uniform thickness of 12.6 μm. The honeycomb-likestructures indicate that the pores are a replica of the ice crystals. Asshown in the high magnification SEM images, the pore sizes are in therange of hundreds nanometers to several micrometers and the pore wallsconsist of thin layers of graphene sheets, which is consistent withtransmission electron microscopy (TEM) results The TEM andhigh-resolution TEM images also reveal that there are many crumpled 5-10nm graphene sheets stacked on the surface of graphene walls that areseveral tens of nanometers thick. This is likely due to rejection fromthe solidification front that pushes the dispersed pre-reduced GO sheetsinto the gaps between the ice crystals formed during the freezingprocess. The clear lattice fringes and typical six-fold symmetrydiffraction pattern provide further evidence for the nearly completereduction of the 3D porous RGO films. The reduction process isassociated with significant changes in the electrical properties of thefilm. For comparison, two electrode I-V conductivity tests were carriedout for GO, pre-reduced GO and 3D porous RGO films, as presented inFIGS. 16 and 17A-D. The GO film exhibits nonlinear and asymmetricbehavior, with a differential conductivity value ranging from x to ydepending on the gate voltage. The pre-reduced GO films shows a morelinear and symmetric curve, with a stable conductivity of 10.3 S/m. The3D porous RGO films give a completely linear I-V curve associated with ahigh conductivity of 1,905 S/m. Because of its high electricalconductivity and continuous open porous structure, the fabricatedgraphene films hold promise as high performance supercapacitorelectrodes. Furthermore, in spite of their highly porous microstructure,the as-prepared 3D porous RGO films exhibited good tensile strength of18.7 MPa.

The unique properties of 3D porous RGO films enable their excellentperformance as supercapacitor electrodes. A symmetric two-electrodesupercapacitor was fabricated by using 3D porous RGO films as the activematerials and 1.0 M H₂SO₄ as the electrolyte. Cyclic voltammetry (CV)curves taken at scan rates from 0.2-20 V/s. They demonstrate that the 3Dporous RGO electrodes retain their rectangular shape and high currentdensities, even at an extremely high scan rate of 20 V/s. Therectangular nature of the CV curves indicates ideal electricaldouble-layer capacitor (EDLC) behavior for the 3D porous RGO films. In acontrol experiment, a stacked RGO film was fabricated via a previousreported method using vacuum filtering of chemically reduced GO sheets.As shown in the cross-section SEM images, the RGO consists of stackedlamellar graphene sheets, which is different from the 3D porous RGOfilms in this work. The schematic illustrations show the easier iondiffusion and minimized electron transport resistance for a 3D porousRGO film compared with an RGO film. The CV and galvanostaticcharge/discharge curves show a significant electrochemical performanceenhancement for the 3D porous RGO films when compared with the RGO filmelectrodes. The more rectangular shape of the CV curves at a high scanrate of 1,000 mV/s and more triangular shape of the galvanostaticcharge/discharge curves at a high current density of 100 A/g indicate abetter capacitive performance and electrolyte ion transport of the 3Dporous RGO electrode. The larger area of the CV curve and longerdischarge time also predict a higher capacitance. The high lineardependence (R2=0.9986) of the discharge current on the scan rate up tohigh scan rates indicates an ultra-high power capability for the 3Dporous RGO electrode. The specific capacitance based on the activematerials of these two supercapacitor electrodes was derived from thegalvanostatic charge/discharge data and is summarized in. The 3D porousRGO film exhibited an ultrahigh gravimetric capacitance of 284.2 F/g ata current density of 1 A/g, and retained ˜61.2% (173.8 F/g) of itsinitial capacitance when the current density was increased up to 500A/g. In contrast, the RGO only had a gravimetric capacitance of 181.3F/g at 1 A/g and a capacitance retention of only 27.8% (50.4 F/g) at 500A/g. The cycling stability of the electrodes was examined by performing10,000 charge/discharge cycles at a current of 25 A/g. The 3D porous RGOfilms exhibited a capacitive retention of 97.6%, which comparesfavorably to the 86.2% shown by the RGO films.

Electrochemical impedance spectroscopy (EIS) is a very useful method toanalyze electrolyte ion transport and other electrochemical behavior.The Nyquist plot of the 3D porous RGO film features a nearly verticalcurve, indicating an ideal capacitive performance. A close-upobservation of the high frequency regime reveals a semicircle with a˜45° Warburg region. The Nyquist plot of the 3D porous RGO electrodeshows a shorter Warburg region and a smaller semicircle, indicating alower charge transfer resistance and more efficient electrolyte iondiffusion when compared to the RGO electrode. In order to betterunderstand the interfacial electrochemical behavior of thesupercapacitors, we fit the Nyquist plots to an equivalent circuit andsummarize the specific values for the different circuit elements. Thedetails of the relationship between the Nyquist plot and the equivalentcircuit are illustrated in the Supplementary EIS Analysis section. Theinternal resistances (Rs) are 0.202 Ω and 0.244 Ω; with charge transportresistances (Rct) of 0.181 Ω and 1.04 Ω obtained by fitting the 3Dporous RGO film and RGO film supercapacitors, respectively. These lowresistance values indicate the high electron conductivity along thegraphene walls and high-speed ion migration through the 3D open pores.The open surfaces of the 3D porous RGO films can be easily accessed byelectrolyte ions without a diffusion limit, which guarantees a largecapacitance at high current density/scan rate. In contrast, thecondensed layer structure of RGO films only provides a narrow neck-likechannel and confined pores for electrolyte ion transport, which resultsin increased resistance and suppressed capacitances. This was furtherconfirmed by Bode plots (FIG. 4i ). The characteristic frequency f0 atthe phase angle of −45° marks the transition point from resistivebehavior to capacitive behavior. The 3D porous RGO supercapacitorexhibits an f0 of 55.7 Hz, which corresponds to a time constant(τ₀=1/f₀) of 17.8 ms, which is significantly lower than 91.7 msexhibited by the RGO supercapacitor. This time constant for the 3Dporous RGO supercapacitor is even lower than some pure carbon basedmicro-supercapacitors e.g. 26 ms for onion-like carbon, and 700 ms foractivated carbon. This extremely low time constant provides furtherevidence for the high-speed ion diffusion and transport inside the 3Dporous RGO electrodes.

The sum of Rs and Rct are the chief contributors to the equivalentseries resistance (ESR), which mainly limits the specific power densityof a supercapacitor. Thus, the low ESR, high capacitance and nearlyideal electrolyte ion transport of the 3D porous RGO electrodes providethe extremely high power density of 282 kW/kg and high energy density of9.9 Wh/kg, even with only a 1.0 V potential window using an aqueouselectrolyte. This high power density from the 3D porous RGOsupercapacitor is close to that of an aluminum electrolytic capacitorand much higher than most previously reported EDLCs, pseudo-capacitors,and even asymmetric supercapacitors. It is worth noting that ourcalculations are based on the power density obtained by dividing theenergy density by the discharging time. This means the value of thepower density is the device has actually been achieved. Some of theextremely high power densities reported previously are calculated fromthe square of the potential window divided by 4 times the ESR, which isthe theoretical ideal maximum power density of a supercapacitor. Theactual highest power density achieved by a supercapacitor is generallymuch lower than this ideal maximum value.

The high loading mass of active materials is a critical factor in thetotal performance of a supercapacitor, as discussed in an earlier paper.Vacuum filtration, the method used in this research to fabricateelectrodes, is a common method for preparing graphene or graphene-basedfilms due to its easy manipulation. One of the advantages of thefiltration method is the convenience in controlling the thickness andmass loading of an as-filtered film simply by adjusting the volume ofthe dispersion used. Thus, in order to increase the electrochemicalperformance of the total device, we increased the loading mass of theactive electrode material by simply increasing the dispersion volume. Ascan be seen in cross-sectional SEM images the as-prepared films maintaintheir highly porous microstructure when the thickness is increased to20.4 μm, i.e. twice the loading (3D porous RGO-2), and to 44.7 μm, afive-fold increase in the loading (3D porous RGO-5). Because of the highelectrical conductivity and excellent ion transport inside the porouselectrodes, the CV curves maintain their rectangular shapes even whenthe scan rate is increased up to 1.0 V/s. The current density increasessignificantly as the loading mass of the 3D porous RGO film isincreased. As a result, the gravimetric capacitance only decreased by6.6% (to 265.5 F/g) and 15% (to 241.5 F/g) at the mass loadings of twiceand five-fold, respectively. Meanwhile, the areal capacitance increasesfrom 56.8 mF/cm² to 109 mF/cm²and 246 mF/cm², respectively.

In order to further evaluate the practical potential of the 3D porousRGO supercapacitors, we calculated the energy density and power densitybased on the total device, which means the values were normalized by thetotal volume including the two electrodes, current collectors,electrolyte and separator. As summarized in a Ragone plot, our devicesexhibit high power densities (7.8-14.3 kW kg-1). Furthermore, byincreasing the mass loading of the active materials, the 3D porous RGOsupercapacitor can store a high energy density up to 1.11 Wh L-1, whichis even comparable to supercapacitors based on organic electrolytes orionic liquids.

The freezing-casting and filtration techniques used in producing 3Dporous graphene films are mainly related to some basic parameters, suchas the shape and size of the original materials, and their surfacetension and dispersibility. Thus, this method could provide a universalpathway to assemble 2D materials into 3D porous macrostructures. Thecurrent method appears more adaptable than previous routes to fabricate3D graphene films, such as a hydrothermal method, CVD, interfacialgelation, and template-directed ordered assembly. The highly porousmicrostructure, high conductivity and strong mechanical properties endowthe 3D porous RGO film with a potential for many applications.

High power density supercapacitors are an ideal application that makesuse of all of the above-mentioned advantages. High power density willcontinue to attract increasing attention, especially for conditions inwhich huge amounts of energy need to be input or output in a limitedtime, such as load-leveling the emerging smart electrical grid, flashcharging electronics and quick acceleration for electric vehicles.However, the power densities of most previously reported supercapacitorsare generally limited by the narrow or confined electrolyte iontransport channels. Our 3D porous RGO films can satisfy the mainrequirements for high power density supercapacitor electrodes. The openand connected pores provide high-speed electrolyte ion transport andfreely accessible graphene surfaces for forming electrical doublelayers. The high electrical conductivity and robust mechanical strengthensure high efficiency in exporting electrons to an outside load.Furthermore, these 3D porous RGO networks can be further scaled-up intheir loading mass and/or thickness due to the controllable filtrationprocess.

In summary, we have developed a method combining freeze-casting andfiltration to effectively synthesize 3D porous graphene films. Thisfacile and scalable fabrication approach could become a general pathwayfor the synthesis of 3D porous films by assembling 2D materials. Ahigh-performance supercapacitor has been fabricated by using these 3Dporous graphene films as the active material. With their highly porousmicrostructure, superior electrical conductivity and exceptionalmechanical strength, the supercapacitor exhibited both very high powerdensities and energy densities. This research could open up excitingopportunities for 3D porous film fabrication and a wide range of highpower density applications.

What is claimed is:
 1. An energy storage device comprising: (a) twoelectrodes, wherein at least one electrode comprises a reduced grapheneoxide film comprising a three-dimensional hierarchy of pores having apore size of less than 1,000 nm, wherein the film has a density of atleast about 0.1 g/cm³; (b) an electrolyte; and (c) an separator disposedbetween the first electrode and the second electrode.
 2. The energystorage device of claim 1, wherein the three-dimensional hierarchy ofpores comprises a honeycomb structure
 3. The energy storage device ofclaim 1, wherein the at least one electrode has a thickness of fromabout 1 μm to about 60 μm.
 4. The energy storage device of claim 1,wherein the separator has a thickness of less than about 16 μm.
 5. Theenergy storage device of claim 1, wherein the separator has apermeability of greater than about 150 sec/100 ml.
 6. The energy storagedevice of claim 1, wherein the separator has a porosity of greater thanabout 35%.
 7. The energy storage device of claim 1, wherein theseparator has a shut-down temperature of less than about 150° C.
 8. Theenergy storage device of claim 1, wherein the separator comprises apolymer comprising neoprene, nylon, polyvinyl chloride, polystyrene,polyethylene, polypropylene, polyacrylonitrile, polyvinyl butyral,silicone, or any combination thereof.
 9. The energy storage device ofclaim 1, wherein the electrolyte comprises an aqueous electrolyte. 10.The energy storage device of claim 9, wherein the aqueous electrolytehas a concentration of at least about 0.5 M.
 11. The energy storagedevice of claim 9, wherein the aqueous electrolyte comprises a strongacid comprising perchloric acid, hydroiodic acid, hydrobromic acid,hydrochloric acid, sulfuric acid, p-toluenesulfonic acid,methanesulfonic acid, or any combination thereof.
 12. The energy storagedevice of claim 1, having a volumetric energy density of at least about0.1 Wh/L.
 13. The energy storage device of claim 1, having a volumetricpower density of at least about 3 kW/L.
 14. The energy storage device ofclaim 1, having a gravimetric power density of at least about 280 kW/kg.15. The energy storage device of claim 1, wherein the reduced grapheneoxide film has an active density of at least about 0.1 g/cm³.
 16. Theenergy storage device of claim 1, wherein the reduced graphene oxidefilm has an areal mass loading of at least about 0.1 mg/cm².
 17. Theenergy storage device of claim 1, wherein the reduced graphene oxidefilm has a tensile strength of at least about 9 MPa.
 18. The energystorage device of claim 1, wherein the reduced graphene oxide film has aconductivity of at least about 1,000 S/m.
 19. The energy storage deviceof claim 1, wherein the reduced graphene oxide film has a capacitiveretention, after about 1000 cycles of charging, of at least about 50%.20. The energy storage device of claim 1, wherein the reduced grapheneoxide film has an areal capacitance of at least about 25 mF/cm².